A key to understanding the Gospel is to first understand the narrative about Paul. The narrative about Paul appears to be partially preserved in Acts of the Apostles. My conclusion is that what we now call the Gospel of Mark is the most well preserved version of the narrative that was created to preface the story about Paul. The Gospel of Luke and Acts appears to have been developed from the larger collection, that consisted of the Gospel followed by the story about Paul followed by the Pauline letter collection.
Notice that in Acts we have the killing of Stephen followed directly by the account of Paul's persecutions and then the conversion of Paul. I think this is reworked from the original flow that lead from the killing of Jesus into the story about Paul. We go from execution to persecution to conversion, which is how the original story went, but it was the execution of Jesus, not Stephen.
So here is an initial attempt at a very crude reconstruct the original story about Paul, which I'll call Acts of the Apostle. This is reconstructed using passages from Acts of the Apostles and content from the Pauline letters, with some minor revisions on my part.
Acts of the Apostle:
A severe persecution began against the assemblies of God in Jerusalem. Paul was ravaging the assemblies by entering house after house; dragging off both men and women, he committed them to prison. Paul was sent to go from Jerusalem to Damascus. As he was going along the road in Galilee, suddenly a light from heaven flashed around him. He fell to the ground and heard a voice saying to him, “Paul, Paul, why do you persecute me?” He asked, “Who are you, Lord?” The reply came, “I am Jesus, whom you are persecuting. But get up and enter the city, and you will be told what you are to do.” The men who were traveling with him stood speechless because they heard the voice but saw no one. Paul got up from the ground, and though his eyes were open, he could see nothing; so they led him by the hand and brought him into Damascus. For three days he was without sight and neither ate nor drank.
A man came to Paul and said, ‘Brother Paul, regain your sight!’ In that very hour I regained my sight and saw him. Then he said, ‘God has chosen you to know his will, to see the Righteous One, and to hear his own voice, for you will be his witness to all the world of what you have seen and heard. And now why do you delay? Get up, be baptized, and have your sins washed away, calling on his name.’
Immediately Paul went to Arabia, where he spread the good news of the Lord, then returned to Damascus.
[Some stuff about Paul meeting Barnabas, Timothy, and Mark, but this has been so thoroughly rewritten in Acts of the Apostles I'm not sure what was said originally.]
During the night Paul had a vision: there stood a man of Macedonia pleading with him and saying, “Come over to Macedonia and help us.” When he had seen the vision, we immediately tried to cross over to Macedonia, being convinced that God had called us to proclaim the good news to them.
We therefore set sail from Troas and took a straight course to Samothrace, the following day to Neapolis, and from there to Philippi, which is a leading city of the district of Macedonia and a Roman colony. We remained in this city for some days. On the Sabbath day we went outside the gate by the river, where we supposed there was a place of prayer, and we sat down and spoke to the women who had gathered there. A certain woman named Lydia, a worshiper of God, was listening to us; she was from the city of Thyatira and a dealer in purple cloth. The Lord opened her heart to listen eagerly to what was said by Paul. When she and her household were baptized, she urged us, saying, “If you have judged me to be faithful to the Lord, come and stay at my home.” And she prevailed upon us.
One day as we were going to the place of prayer, we met a female slave who had a spirit of divination and brought her owners a great deal of money by fortune-telling. While she followed Paul and us, she would cry out, “These men are slaves of the Most High God, who proclaim to you the way of salvation.” She kept doing this for many days. But Paul, very much annoyed, turned and said to the spirit, “I order you in the name of Jesus Christ to come out of her.” And it came out that very hour.
[...Some activities about Paul's continuing mission. He may or may not have been put into jail at this point, as happens in Acts of the Apostles...]
Now after these things had been accomplished, Paul resolved in the Spirit to go through Macedonia and Achaia and then to go on to Jerusalem. So he sent two of his helpers, Timothy and Erastus, to Macedonia, while he himself stayed for some time longer in Asia.
...
After the uproar had ceased, Paul sent for the disciples, and after encouraging them and saying farewell, he left for Macedonia. When he had gone through those regions and had given them much encouragement, he came to Greece, where he stayed for three months. He was about to set sail for Syria when a plot was made against him by the Jews, so he decided to return through Macedonia. He was accompanied by Sopater son of Pyrrhus from Beroea, by Aristarchus and Secundus from Thessalonica, by Gaius from Derbe, and by Timothy, as well as by Tychicus and Trophimus from Asia. They went ahead and were waiting for us in Troas, but we sailed from Philippi after the days of Unleavened Bread, and in five days we joined them in Troas, where we stayed for seven days.
On the first day of the week, when we met to break bread, Paul was holding a discussion with them; since he intended to leave the next day, he continued speaking until midnight. There were many lamps in the room upstairs where we were meeting. A young man named Eutychus, who was sitting in the window, began to sink off into a deep sleep while Paul talked still longer. Overcome by sleep, he fell to the ground three floors below and was picked up dead. But Paul went down and bending over him took him in his arms and said, “Do not be alarmed, for his life is in him.” Then Paul went upstairs, and after he had broken bread and eaten, he continued to converse with them until dawn; then he left. Meanwhile they had taken the boy away alive and were not a little comforted.
We went ahead to the ship and set sail for Assos, intending to take Paul on board there, for he had made this arrangement, intending to go by land himself. When he met us in Assos, we took him on board and went to Mitylene. We sailed from there, and on the following day we arrived opposite Chios. The next day we touched at Samos, and the day after that we came to Miletus. For Paul had decided to sail past Ephesus, so that he might not have to spend time in Asia; he was eager to be in Jerusalem, if possible, on the day of Pentecost.
...
After these days we got ready and started to go up to Jerusalem. Some of the disciples from Caesarea also came along and brought us to the house of Mnason of Cyprus, an early disciple, with whom we were to stay.
When we arrived in Jerusalem, the brothers welcomed us. The next day Paul went with us to visit James, and all the elders were present. After greeting them, he related one by one the things that God had done among the gentiles through his ministry. Some of those present complained that Titus was not circumcised, but Paul did not submit to them. Paul proclaimed that gospel of Jesus Christ, that no longer were there distinctions between Greeks, Jews and barbarians. Seeing that Paul did not support the law, James, Peter and John, the supposed pillars, agreed that Paul should continue his work among the gentiles. They asked only one thing, that we remember the poor, which were were eager to do. So we left to return to Asia.
Peter came to Antioch while we were still there. Paul saw that Peter was no longer eating with the gentiles and that he only associated with those who were circumcised. So Paul confronted Peter and asked him why he was still following the law, since the Lord had declared that there were no longer distinctions between Jews and gentiles. Peter knew that he had been led astray into the hypocrisy of James and John.
...
While Apollos was in Corinth, Paul passed through the interior regions and came to Ephesus, where he found some disciples. He said to them, “Did you receive the Holy Spirit when you became believers?” They replied, “No, we have not even heard that there is a Holy Spirit.” Then he said, “Into what, then, were you baptized?” They answered, “Into John’s baptism.” Paul said, “John baptized with the baptism of repentance, telling the people to believe in the one who was to come after him.” On hearing this, they were baptized in the name of the Lord Jesus. When Paul had laid his hands on them, the Holy Spirit came upon them, and they spoke in tongues and prophesied, altogether there were about twelve of them.
...
When we had parted from them and set sail, we came by a straight course to Cos, and the next day to Rhodes, and from there to Patara. When we found a ship bound for Phoenicia, we went on board and set sail. We came in sight of Cyprus, and leaving it on our left, we sailed to Syria and landed at Tyre, because the ship was to unload its cargo there. We looked up the disciples and stayed there for seven days. Through the Spirit they told Paul not to go on to Jerusalem. When our days there were ended, we left and proceeded on our journey, and all of them, with wives and children, escorted us outside the city. There we knelt down on the beach and prayed and said farewell to one another. Then we went on board the ship, and they returned home.
When we had finished the voyage from Tyre, we arrived at Ptolemais, and we greeted the brothers and sisters and stayed with them for one day. The next day we left and came to Caesarea, and we went into the house of Philip the evangelist, one of the seven, and stayed with him. He had four unmarried daughters who had the gift of prophecy. While we were staying there for several days, a prophet named Agabus came down from Judea. He came to us and took Paul’s belt, bound his own feet and hands with it, and said, “Thus says the Holy Spirit, ‘This is the way the Jews in Jerusalem will bind the man who owns this belt and will hand him over to the gentiles.’ ” When we heard this, we and the people there urged him not to go up to Jerusalem. Then Paul answered, “What are you doing, weeping and breaking my heart? For I am ready not only to be bound but even to die in Jerusalem for the name of the Lord Jesus.” Since he would not be persuaded, we remained silent except to say, “The Lord’s will be done.”
...
When we arrived in Jerusalem Paul went to the temple. Jews from Asia, who had seen him in the temple, stirred up the whole crowd. They seized him, shouting, “Fellow Israelites, help! This is the man who is teaching everyone everywhere against our people, our law, and this place; more than that, he has actually brought Greeks into the temple and has defiled this holy place.” For they had previously seen Trophimus the Ephesian with him in the city, and they supposed that Paul had brought him into the temple. Then all the city was aroused, and the people rushed together. They seized Paul and dragged him out of the temple, and immediately the doors were shut. While they were trying to kill him, word came to the tribune of the cohort that all Jerusalem was in an uproar. Immediately he took soldiers and centurions and ran down to them. When they saw the tribune and the soldiers, they stopped beating Paul. Then the tribune came, arrested him, and ordered him to be bound with two chains; he inquired who he was and what he had done. Some in the crowd shouted one thing, some another, and as he could not learn the facts because of the uproar, he ordered him to be brought into the barracks. When Paul came to the steps, the violence of the mob was so great that he had to be carried by the soldiers. The crowd that followed kept shouting, “Away with him!”
The soldiers delivered Paul to the Sanhedrin - the Jewish council.
The Jews from Asia followed Paul to the council. They told the high priest that Paul was teaching against the law. They told them that Paul's companions were not circumcised adn that he had brought them into the temple.
The high priest asked Paul if this was true. While Paul was looking intently at the council he said, “Brothers, up to this day I have lived my life with a clear conscience before God.” Then the high priest Ananias ordered those standing near him to strike him on the mouth. At this Paul said to him, “God will strike you, you whitewashed wall! Are you sitting there to judge me according to the law, and yet in violation of the law you order me to be struck?” Those standing nearby said, “Do you dare to insult God’s high priest?” And Paul said, “I did not realize, brothers, that he was high priest, for it is written, ‘You shall not speak evil of a leader of your people.’ ”
When Paul noticed that some were Sadducees and others were Pharisees, he called out in the council, “Brothers, I am a Pharisee, a son of Pharisees. I am on trial concerning the hope of the resurrection of the dead.” When he said this, a dissension began between the Pharisees and the Sadducees, and the assembly was divided. (The Sadducees say that there is no resurrection or angel or spirit, but the Pharisees acknowledge all three.) Then a great clamor arose, and certain scribes of the Pharisees’ group stood up and contended, “We find nothing wrong with this man. What if a spirit or an angel has spoken to him?” When the dissension became violent, the tribune, fearing that they would tear Paul to pieces, ordered the soldiers to go down, take him by force, and bring him into the barracks.
That night the Lord stood near him and said, “Keep up your courage! For just as you have testified for me in Jerusalem, so you must bear witness also in Rome.”
In the morning the Jews joined in a conspiracy and bound themselves by an oath neither to eat nor drink until they had killed Paul. There were more than forty who joined in this conspiracy. They went to the chief priests and elders and said, “We have strictly bound ourselves by an oath to taste no food until we have killed Paul. Now then, you and the council must notify the tribune to bring him down to you, on the pretext that you want to make a more thorough examination of his case. And we are ready to do away with him before he arrives.”
...
[Goes on to tell of Paul's voyage to Rome]
A severe persecution began against the assemblies of God in Jerusalem. Paul was ravaging the assemblies by entering house after house; dragging off both men and women, he committed them to prison. Paul was sent to go from Jerusalem to Damascus. As he was going along the road in Galilee, suddenly a light from heaven flashed around him. He fell to the ground and heard a voice saying to him, “Paul, Paul, why do you persecute me?” He asked, “Who are you, Lord?” The reply came, “I am Jesus, whom you are persecuting. But get up and enter the city, and you will be told what you are to do.” The men who were traveling with him stood speechless because they heard the voice but saw no one. Paul got up from the ground, and though his eyes were open, he could see nothing; so they led him by the hand and brought him into Damascus. For three days he was without sight and neither ate nor drank.
A man came to Paul and said, ‘Brother Paul, regain your sight!’ In that very hour I regained my sight and saw him. Then he said, ‘God has chosen you to know his will, to see the Righteous One, and to hear his own voice, for you will be his witness to all the world of what you have seen and heard. And now why do you delay? Get up, be baptized, and have your sins washed away, calling on his name.’
Immediately Paul went to Arabia, where he spread the good news of the Lord, then returned to Damascus.
[Some stuff about Paul meeting Barnabas, Timothy, and Mark, but this has been so thoroughly rewritten in Acts of the Apostles I'm not sure what was said originally.]
During the night Paul had a vision: there stood a man of Macedonia pleading with him and saying, “Come over to Macedonia and help us.” When he had seen the vision, we immediately tried to cross over to Macedonia, being convinced that God had called us to proclaim the good news to them.
We therefore set sail from Troas and took a straight course to Samothrace, the following day to Neapolis, and from there to Philippi, which is a leading city of the district of Macedonia and a Roman colony. We remained in this city for some days. On the Sabbath day we went outside the gate by the river, where we supposed there was a place of prayer, and we sat down and spoke to the women who had gathered there. A certain woman named Lydia, a worshiper of God, was listening to us; she was from the city of Thyatira and a dealer in purple cloth. The Lord opened her heart to listen eagerly to what was said by Paul. When she and her household were baptized, she urged us, saying, “If you have judged me to be faithful to the Lord, come and stay at my home.” And she prevailed upon us.
One day as we were going to the place of prayer, we met a female slave who had a spirit of divination and brought her owners a great deal of money by fortune-telling. While she followed Paul and us, she would cry out, “These men are slaves of the Most High God, who proclaim to you the way of salvation.” She kept doing this for many days. But Paul, very much annoyed, turned and said to the spirit, “I order you in the name of Jesus Christ to come out of her.” And it came out that very hour.
[...Some activities about Paul's continuing mission. He may or may not have been put into jail at this point, as happens in Acts of the Apostles...]
Now after these things had been accomplished, Paul resolved in the Spirit to go through Macedonia and Achaia and then to go on to Jerusalem. So he sent two of his helpers, Timothy and Erastus, to Macedonia, while he himself stayed for some time longer in Asia.
...
After the uproar had ceased, Paul sent for the disciples, and after encouraging them and saying farewell, he left for Macedonia. When he had gone through those regions and had given them much encouragement, he came to Greece, where he stayed for three months. He was about to set sail for Syria when a plot was made against him by the Jews, so he decided to return through Macedonia. He was accompanied by Sopater son of Pyrrhus from Beroea, by Aristarchus and Secundus from Thessalonica, by Gaius from Derbe, and by Timothy, as well as by Tychicus and Trophimus from Asia. They went ahead and were waiting for us in Troas, but we sailed from Philippi after the days of Unleavened Bread, and in five days we joined them in Troas, where we stayed for seven days.
On the first day of the week, when we met to break bread, Paul was holding a discussion with them; since he intended to leave the next day, he continued speaking until midnight. There were many lamps in the room upstairs where we were meeting. A young man named Eutychus, who was sitting in the window, began to sink off into a deep sleep while Paul talked still longer. Overcome by sleep, he fell to the ground three floors below and was picked up dead. But Paul went down and bending over him took him in his arms and said, “Do not be alarmed, for his life is in him.” Then Paul went upstairs, and after he had broken bread and eaten, he continued to converse with them until dawn; then he left. Meanwhile they had taken the boy away alive and were not a little comforted.
We went ahead to the ship and set sail for Assos, intending to take Paul on board there, for he had made this arrangement, intending to go by land himself. When he met us in Assos, we took him on board and went to Mitylene. We sailed from there, and on the following day we arrived opposite Chios. The next day we touched at Samos, and the day after that we came to Miletus. For Paul had decided to sail past Ephesus, so that he might not have to spend time in Asia; he was eager to be in Jerusalem, if possible, on the day of Pentecost.
...
After these days we got ready and started to go up to Jerusalem. Some of the disciples from Caesarea also came along and brought us to the house of Mnason of Cyprus, an early disciple, with whom we were to stay.
When we arrived in Jerusalem, the brothers welcomed us. The next day Paul went with us to visit James, and all the elders were present. After greeting them, he related one by one the things that God had done among the gentiles through his ministry. Some of those present complained that Titus was not circumcised, but Paul did not submit to them. Paul proclaimed that gospel of Jesus Christ, that no longer were there distinctions between Greeks, Jews and barbarians. Seeing that Paul did not support the law, James, Peter and John, the supposed pillars, agreed that Paul should continue his work among the gentiles. They asked only one thing, that we remember the poor, which were were eager to do. So we left to return to Asia.
Peter came to Antioch while we were still there. Paul saw that Peter was no longer eating with the gentiles and that he only associated with those who were circumcised. So Paul confronted Peter and asked him why he was still following the law, since the Lord had declared that there were no longer distinctions between Jews and gentiles. Peter knew that he had been led astray into the hypocrisy of James and John.
...
While Apollos was in Corinth, Paul passed through the interior regions and came to Ephesus, where he found some disciples. He said to them, “Did you receive the Holy Spirit when you became believers?” They replied, “No, we have not even heard that there is a Holy Spirit.” Then he said, “Into what, then, were you baptized?” They answered, “Into John’s baptism.” Paul said, “John baptized with the baptism of repentance, telling the people to believe in the one who was to come after him.” On hearing this, they were baptized in the name of the Lord Jesus. When Paul had laid his hands on them, the Holy Spirit came upon them, and they spoke in tongues and prophesied, altogether there were about twelve of them.
...
When we had parted from them and set sail, we came by a straight course to Cos, and the next day to Rhodes, and from there to Patara. When we found a ship bound for Phoenicia, we went on board and set sail. We came in sight of Cyprus, and leaving it on our left, we sailed to Syria and landed at Tyre, because the ship was to unload its cargo there. We looked up the disciples and stayed there for seven days. Through the Spirit they told Paul not to go on to Jerusalem. When our days there were ended, we left and proceeded on our journey, and all of them, with wives and children, escorted us outside the city. There we knelt down on the beach and prayed and said farewell to one another. Then we went on board the ship, and they returned home.
When we had finished the voyage from Tyre, we arrived at Ptolemais, and we greeted the brothers and sisters and stayed with them for one day. The next day we left and came to Caesarea, and we went into the house of Philip the evangelist, one of the seven, and stayed with him. He had four unmarried daughters who had the gift of prophecy. While we were staying there for several days, a prophet named Agabus came down from Judea. He came to us and took Paul’s belt, bound his own feet and hands with it, and said, “Thus says the Holy Spirit, ‘This is the way the Jews in Jerusalem will bind the man who owns this belt and will hand him over to the gentiles.’ ” When we heard this, we and the people there urged him not to go up to Jerusalem. Then Paul answered, “What are you doing, weeping and breaking my heart? For I am ready not only to be bound but even to die in Jerusalem for the name of the Lord Jesus.” Since he would not be persuaded, we remained silent except to say, “The Lord’s will be done.”
...
When we arrived in Jerusalem Paul went to the temple. Jews from Asia, who had seen him in the temple, stirred up the whole crowd. They seized him, shouting, “Fellow Israelites, help! This is the man who is teaching everyone everywhere against our people, our law, and this place; more than that, he has actually brought Greeks into the temple and has defiled this holy place.” For they had previously seen Trophimus the Ephesian with him in the city, and they supposed that Paul had brought him into the temple. Then all the city was aroused, and the people rushed together. They seized Paul and dragged him out of the temple, and immediately the doors were shut. While they were trying to kill him, word came to the tribune of the cohort that all Jerusalem was in an uproar. Immediately he took soldiers and centurions and ran down to them. When they saw the tribune and the soldiers, they stopped beating Paul. Then the tribune came, arrested him, and ordered him to be bound with two chains; he inquired who he was and what he had done. Some in the crowd shouted one thing, some another, and as he could not learn the facts because of the uproar, he ordered him to be brought into the barracks. When Paul came to the steps, the violence of the mob was so great that he had to be carried by the soldiers. The crowd that followed kept shouting, “Away with him!”
The soldiers delivered Paul to the Sanhedrin - the Jewish council.
The Jews from Asia followed Paul to the council. They told the high priest that Paul was teaching against the law. They told them that Paul's companions were not circumcised adn that he had brought them into the temple.
The high priest asked Paul if this was true. While Paul was looking intently at the council he said, “Brothers, up to this day I have lived my life with a clear conscience before God.” Then the high priest Ananias ordered those standing near him to strike him on the mouth. At this Paul said to him, “God will strike you, you whitewashed wall! Are you sitting there to judge me according to the law, and yet in violation of the law you order me to be struck?” Those standing nearby said, “Do you dare to insult God’s high priest?” And Paul said, “I did not realize, brothers, that he was high priest, for it is written, ‘You shall not speak evil of a leader of your people.’ ”
When Paul noticed that some were Sadducees and others were Pharisees, he called out in the council, “Brothers, I am a Pharisee, a son of Pharisees. I am on trial concerning the hope of the resurrection of the dead.” When he said this, a dissension began between the Pharisees and the Sadducees, and the assembly was divided. (The Sadducees say that there is no resurrection or angel or spirit, but the Pharisees acknowledge all three.) Then a great clamor arose, and certain scribes of the Pharisees’ group stood up and contended, “We find nothing wrong with this man. What if a spirit or an angel has spoken to him?” When the dissension became violent, the tribune, fearing that they would tear Paul to pieces, ordered the soldiers to go down, take him by force, and bring him into the barracks.
That night the Lord stood near him and said, “Keep up your courage! For just as you have testified for me in Jerusalem, so you must bear witness also in Rome.”
In the morning the Jews joined in a conspiracy and bound themselves by an oath neither to eat nor drink until they had killed Paul. There were more than forty who joined in this conspiracy. They went to the chief priests and elders and said, “We have strictly bound ourselves by an oath to taste no food until we have killed Paul. Now then, you and the council must notify the tribune to bring him down to you, on the pretext that you want to make a more thorough examination of his case. And we are ready to do away with him before he arrives.”
...
[Goes on to tell of Paul's voyage to Rome]
This narrative contains many elements that were then used by the writer of the first Gospel. This narrative was written before the Gospel. It opens by narrating what is described in the opening of the letter to the Galatians. The first Gospel was designed to lead into this narrative, which is why the original ending of the Gospel of Mark concludes without anyone seeing the risen Jesus and without the disciples having knowledge of the message of Jesus to meet him in Galilee. The writer of the Gospel crafted that ending to set the stage for beginning of the narrative about Paul, in which Jesus appears to Paul alone.
It is also from this narrative that the writer of the Gospel got the figure of John, who became "John the Baptist". Except I think that in this narrative, "John" is "John the pillar".
The writer of the Gospel has created two characters from "John the pillar". The first is James and John Zebedee, who represent the pillars, along with Peter. But the writer introduced John who baptizes as a different person, perhaps not realizing that this John was supposed to be the same person as John the pillar. But it is likely that this John was not given the title "the Baptist" in the original Gospel, that was a later addition, which is why John does not have the title "the Baptist" in several other works, such as the Gospel of John and parts of Luke. Also, the part in Mark 6 about John being killed by Herod is a later addition and was not part of the original narrative.
The main flow of the Gospel narrative comes from emulating the story about Paul. It was the story about Paul that first had the theme of Paul rounding up a collection of followers, traveling back and fourth across sea between Jewish and gentile communities, then ultimately to Jerusalem where he was arrested and put on trial. Except in Paul's story, when he was "handed over to the gentiles", they rescued him from the Jews as opposed to committing his execution.
While what I've attempted to piece together here is very speculative, I think the main points are that the original story about Paul included these key elements:
1) The appearance of Jesus to Paul, which led to his conversion.
2) Paul engaging in a ministry and gaining followers who traveled with him.
3) Paul meeting with Peter, James and John in Jerusalem but being in conflict with them.
4) Paul baptizing someone who had only known "the baptism of John" (the pillar).
5) Paul going to the temple in Jerusalem and then being arrested there.
6) Paul being put on trial in Jerusalem for teaching against the law.
7) Paul being "freed" by being "handed over to the gentiles".
The writer of the Gospel used this as the template for his story.
