For the moment let's stick with the fact that the place where this incident (either called 'the Good Samaritan' pericope or the beginning of the gospel associated with the Marcionites) occurs at Adumim or a place associated with Adam. We saw Origen, now Irenaeus writes:
The footnote in Briggman " Suum hominem, a singular form which I take as a collective reference to human beings as the creation of the Word, see also AH 3.24.1: hominem suum."
In other words, Adam = the fallen man.
It was necessary, therefore, that the Lord, coming to the lost sheep, and making recapitulation of so comprehensive a dispensation, and seeking after His own handiwork, should save that very man who had been created after His image and likeness, that is, Adam, filling up the times of His condemnation, which had been incurred through disobedience,--[times] "which the Father had placed in His own power."(11) [This was necessary,] too, inasmuch as the whole economy of salvation regarding man came to pass according to the good pleasure of the Father, in order that God might not be conquered, nor His wisdom lessened, [in the estimation of His creatures.] For if man, who had been created by God that he might live, after losing life, through being injured by the serpent that had corrupted him, should not any more return to life, but should be utterly [and for ever] abandoned to death, God would [in that case] have been conquered, and the wickedness of the serpent would have prevailed over the will of God. But inasmuch as God is invincible and long- suffering, He did indeed show Himself to be long-suffering in the matter of the correction of man and the probation of all, as I have already observed; and by means of the second man did He bind the strong man, and spoiled his goods,(1) and abolished death, vivifying that man who had been in a state of death. For at the first Adam became a vessel in his (Satan's) possession, whom he did also hold under his power, that is, by bringing sin on him iniquitously, and under colour of immortality entailing death upon him. For, while promising that they should be as gods, which was in no way possible for him to be, he wrought death in them: wherefore he who had led man captive, was justly captured in his turn by God; but man, who had been led captive, was loosed from the bonds of condemnation.
2. But this is Adam, if the truth should be told, the first formed man, of whom the Scripture says that the Lord spake, "Let Us make man after Our own image and likeness;"(2) and we are all from him: and as we are from him, therefore have we all inherited his title. But inasmuch as man is saved, it is fitting that he who was created the original man should be saved. For it is too absurd to maintain, that he who was so deeply injured by the enemy, and was the first to suffer captivity, was not rescued by Him who conquered the enemy, but that his children were,--those whom he had begotten in the same captivity. Neither would the enemy appear to be as yet conquered, if the old spoils remained with him. To give an illustration: If a hostile force had overcome certain [enemies], had bound them, and led them away captive, and held them for a long time in servitude, so that they begat children among them; and somebody, compassionating those who had been made slaves, should overcome this same hostile force; he certainly would not act equitably, were he to liberate the children of those who had been led captive, from the sway of those who had enslaved their fathers, but should leave these latter, who had suffered the act of capture, subject to their enemies,--those, too, on whose very account he had proceeded to this retaliation,--the children succeeding to liberty through the avenging of their fathers' cause, but not(3) so that their fathers, who suffered the act of capture itself, should be left [in bondage]. For God is neither devoid of power nor of justice, who has afforded help to man, and restored him to His own liberty.
3. It was for this reason, too, that immediately after Adam had transgressed, as the Scripture relates, He pronounced no curse against Adam personally, but against the ground, in reference to his works, as a certain person among the ancients has observed: "God did indeed transfer the curse to the earth, that it might not remain in man."(4) But man received, as the punishment of his transgression, the toilsome task of tilling the earth, and to eat bread in the sweat of his face, and to return to the dust from whence he was taken. Similarly also did the woman [receive] toil, and labour, and groans, and the pangs of parturition, and a state of subjection, that is, that she should serve her husband; so that they should neither perish altogether when cursed by God, nor, by remaining unreprimanded, should be led to despise God. But the curse in all its fulness fell upon the serpent, which had beguiled them. "And God," it is declared, "said to the serpent: Because thou hast done this, cubed art thou above all cattle, and above all the beasts of the earth."(5) And this same thing does the Lord also say in the Gospel, to those who are found upon the left hand: "Depart from me, ye cursed, into ever: lasting fire, which my Father hath prepared for the devil and his angels;"(6) indicating that eternal fire was not originally prepared for man, but for him who beguiled man, and caused him to offend--for him, I say, who is chief of the apostasy, and for those angels who became apostates along with him; which [fire], indeed, they too shall justly feel, who, like him, persevere in works of wickedness, without repentance, and without retracing their steps.
4. [These act](7) as Cain [did, who], when he was counselled by God to keep quiet, because he had not made an equitable division of that share to which his brother was entitled, but with envy and malice thought that he could domineer over him, not only did not acquiesce, but even added sin to sin, indicating his state of mind by his action. For what he had planned, that did he also put in practice: he tyrannized over and slew him; God subjecting the just to the unjust, that the former might be proved as the just one by the things which he suffered, and the latter detected as the unjust by those which he perpetrated. And he was not softened even by this, nor did he stop short with that evil deed; but being asked where his brother was, he said, "I know not; am I my brother's keeper?" extending and aggravating [his] wickedness by his answer. For if it is wicked to slay a brother, much worse is it thus insolently and irreverently to reply to the omniscient God as if he could battle Him. And for this he did himself bear a curse about with him, because he gratuitously brought an offering of sin, having had no reverence for God, nor being put to confusion by the act of fratricide.(1)
5. The case of Adam, however, had no analogy with this, but was altogether different. For, having been beguiled by another under the pretext of immortality, he is immediately seized with terror, and hides himself; not as if he were able to escape from God; but, in a state of confusion at having transgressed His command, he feels unworthy to appear before and to hold converse with God. Now, "the fear of the Lord is the beginning of wisdom;"(2) the sense of sin leads to repentance, and God bestows His compassion upon those who are penitent. For [Adam] showed his repentance by his conduct, through means of the girdle [which he used], covering himself with fig-leaves, while there were many other leaves, which would have irritated his body in a less degree. He, however, adopted a dress conformable to his disobedience, being awed by the fear of God; and resisting the erring, the lustful propensity of his flesh (since he had lost his natural disposition and child-like mind, and had come to the knowledge of evil things), he girded a bridle of continence upon himself and his wife, fearing God, and waiting for His coming, and indicating, as it were, some such thing [as follows]: Inasmuch as, he says, I have by disobedience lost that robe of sanctity which I had from the Spirit, I do now also acknowledge that I am deserving of a covering of this nature, which affords no gratification, but which gnaws have retained this clothing for ever, thus humbling himself, if God, who is merciful, had not clothed them with tunics of skins instead of fig-leaves. For this purpose, too, He interrogates them, that the blame might light upon the woman; and again, He interrogates her, that she might convey the blame to the serpent. For she related what had occurred. "The serpent," says she, "beguiled me, and I did eat."(3) But He put no question to the serpent; for He knew that he had been the prime mover in the guilty deed; but He pronounced the curse upon him in the first instance, that it might fall upon man with a mitigated rebuke. For God detested him who had led man astray, but by degrees, and little by little, He showed compassion to him who had been beguiled.
6. Wherefore also He drove him out of Paradise, and removed him far from the tree of life, not because He envied him the tree of life, as some venture to assert, but because He pitied him, [and did not desire] that he should continue a sinner for ever, nor that the sin which surrounded him should be immortal, and evil interminable and irremediable. But He set a bound to his [state of] sin, by interposing death, and thus causing sin to cease,(4) putting an end to it by the dissolution of the flesh, which should take place in the earth, so that man, ceasing at length to live to sin, and dying to it, might begin to live to God.
7. For this end did He put enmity between the serpent and the woman and her seed, they keeping it up mutually: He, the sole of whose foot should be bitten, having power also to tread upon the enemy's head; but the other biting, killing, and impeding the steps of man, until the seed did come appointed to tread down his head,--which was born of Mary, of whom the prophet speaks: "Thou shalt tread upon the asp and the basilisk; thou shalt trample down the lion and the dragon;"(3)-- indicating that sin, which was set up and spread out against man, and which rendered him subject to death, should be deprived of its power, along with death, which rules [over men]; and that the lion, that is, antichrist, rampant against mankind in the latter days, should be trampled down by Him; and that He should bind "the dragon, that old serpent"(6) and subject him to the power of man, who had been conquered(7) so that all his might should be trodden down. Now Adam had been conquered, all life having been taken away from him: wherefore, when the foe was conquered in his turn, Adam received new life; and the last enemy, death, is destroyed,(8) which at the first had taken possession of man. Therefore, when man has been liberated, "what is written shall come to pass, Death is swallowed up in victory. O death sting?"(9) This could not be said with justice, if that man, over whom death did first obtain dominion, were not set free. For his salvation is death's destruction. When therefore the Lord vivifies man, that is, Adam, death is at the same time destroyed.
8. All therefore speak falsely who disallow his (Adam's) salvation, shutting themselves out from life for ever, in that they do not believe that the sheep which had perished has been found.(10) For if it has not been found, the whole human race is still held in a state of perdition. False, therefore, is that, man who first started this idea, or rather, this ignorance and blindness--Tatian.(11) As I have already indicated, this man entangled himself with all the heretics.(1) This dogma, however, has been invented by himself, in order that, by introducing something new, independently of the rest, and by speaking vanity. he might acquire for himself hearers void of faith, affecting to be esteemed a teacher, and endeavouring from time to time to employ sayings of this kind often [made use of] by Paul: "In Adam we all die;"(2) ignorant, however, that "where sin abounded, grace did much more abound."(3) Since this, then, has been clearly shown, let all his disciples be put to shame, and let them wrangle(4) about Adam, as if some great gain were to accrue to them if he be not saved; when they profit nothing more [by that], even as the serpent also did not profit when persuading man [to sin], except to this effect, that he proved him a transgressor, obtaining man as the first-fruits of his own apostasy.(5) But he did not know God's power.(6) Thus also do those who disallow Adam's salvation gain nothing, except this, that they render themselves heretics and apostates from the truth, and show themselves patrons of the serpent and of death.
1. Thus, then, have all these men been exposed, who bring in impious doctrines regarding our Maker and Framer, who also formed this world. and above whom there is no other God and those have been overthrown by their own arguments who teach falsehoods regarding the substance of our Lord, and the dispensation which He fulfilled for the sake of His own creature man. But [it has, on the other hand, been shown], that the preaching of the Church is everywhere consistent, and continues in an even course, and receives testimony from the prophets, the apostles, and all the disciples--as I have proved--through [those in] the beginning, the middle, and the end,(7) and through the entire dispensation of God, and that well-grounded system which tends(8) to man's salvation, namely, our faith; which, having been received from the Church, we do preserve, and which always, by the Spirit of God, renewing its youth, as if it were some precious deposit in an excellent vessel, causes the vessel itself containing it to renew its youth also. For this gift of God has been entrusted to the Church, as breath was to the first created man,(9) for this purpose, that all the members receiving it may be vivified; and the [means of] communion with Christ has been distributed throughout it, that is, the Holy Spirit, the earnest of incorruption, the means of confirming our faith, and the ladder of ascent to God. "
To me at least Irenaeus seems to know about a gospel which began with Jesus descending from heaven to rescue 'Adam.' I think that is important to emphasize. It is not as if Irenaeus doesn't know a context for the heretical gospel alluded to in the British Museum. He does. It is as if the canonical four with their alternative ordering comes after this gospel. That this gospel had widespread familiarity among Christians and explains why early Christians understood Jesus to have come to redeem the lost sheep, Adam. Mary Magdalene etc.