Once we accept that originality of the understanding that Jesus was not the 'son of David' but rather than ONLY the Son of God the question naturally arises - why did the identification of Jesus as 'son of David' ORIGINALLY EXPLICITLY DENIED IN THE GOSPEL come to obscure the original identification of him as 'the Son of God' who visited with the Patriarchs and was depicted active in the world in the Jewish Scriptures? One reason which emerges from the treatise entitled Against Praxeas (again not originally written by Tertullian by transcribed by him from a lost Greek exemplar) is that the traditional emphasis of Jesus as 'the Son of God' brought Christianity into conflict with a monarchian understanding of the Godhead. By emphasizing the humanity of Jesus it helped make the conflicts of a passive Father and an active Son in the universe with the idea of a monarchy in heaven.
The 'son of David' formula imagines that the Son of God essentially lay dormant while Jesus was placed in the womb of Mary and grew into maturity only to assume the throne in heaven (again) after the resurrection. Now the tables have turned. The Father must have been active in the universe and the Son a passive 'instrument' for at least this period - it was reasoned. To this end, it was easier to argue that the Father must also have been active in the universe BEFORE the Incarnation too given that 'fact' that God always remained consistent with himself and his actions never changing.
To this end it is interesting to look at the arguments of the author of Against Praxeas as a lost glimmer of the tradition understanding of the gospel especially the blind man narrative and Jesus's exegesis of Psalm 110:1. Under this scenario, not only was Jesus active in the universe as the Son throughout the gospel the author argues that he constantly gives clues as to the existence of a separate and distinct second power in heaven. Consider the following in light of this argument. The author - who bears a striking resemblance to what we know of Apelles the Marcionite - is making a defense of the tradition understanding of the gospel (i.e. a wholly divine Jesus) and that such an understanding was still in keeping with venerating a monarchy in heaven. We read:
Look to it then, that it be not you rather who are destroying the Monarchy, when you overthrow the arrangement and dispensation of it, which has been constituted in just as many names as it has pleased God to employ. But it remains so firm and stable in its own state, notwithstanding the introduction into it of the Trinity, that the Son actually has to restore it entire to the Father; even as the apostle says in his epistle, concerning the very end of all: "When He shall have delivered up the kingdom to God, even the Father; for He must reign till He hath put all enemies under His feet; "34 following of course the words of the Psalm: "Sit Thou on my right hand, until I make Thine enemies Thy footstool."35 "When, however, all things shall be subdued to Him, (with the exception of Him who did put all things under Him, ) then shall the Son also Himself be subject unto Him who put all things under Him, that God may be all in all."36 We thus see that the Son is no obstacle to the Monarchy, although it is now administered by37 the Son; because with the Son it is still in its own state, and with its own state will be restored to the Father by the Son. No one, therefore, will impair it, on account of admitting the Son (to it), since it is certain that it has been committed to Him by the Father, and by and by has to be again delivered up by Him to the Father. Now, from this one passage of the epistle of the inspired apostle, we have been already able to show that the Father and the Son are two separate Persons, not only by the mention of their separate names as Father and the Son, but also by the fact that He who delivered up the kingdom, and He to whom it is delivered up-and in like manner, He who subjected (all things), and He to whom they were subjected-must necessarily be two different Beings.
But almost all the Psalms which prophesy of120 the person of Christ, represent the Son as conversing with the Father-that is, represent Christ (as speaking) to God. Observe also the Spirit speaking of the Father and the Son, in the character of121 a third Person: "The Lord said unto my Lord, Sit Thou on my right hand, until I make Thine enemies Thy footstool. "122 Likewise in the words of Isaiah: "Thus saith the Lord to the Lord123 mine Anointed. "124 Likewise, in the same prophet, He says to the Father respecting the Son: "Lord, who hath believed our report, and to whom is the arm of the Lord revealed? We brought a report concerning Him, as if He were a little child, as if He were a root in a dry ground, who had no form nor comeliness."125 These are a few testimonies out of many; for we do not pretend to bring up all the passages of Scripture, because we have a tolerably large accumulation of them in the various heads of our subject, as we in our several chapters call them in as our witnesses in the fulness of their dignity and authority.
Accordingly, Isaiah also says to the Person of Christ: "The Sabaeans, men of stature, shall pass over to Thee; and they shall follow after Thee, bound in fetters; and they shall worship Thee, because God is in Thee: for Thou art our God, yet we knew it not; Thou art the God of Isreal."141 For here too, by saying, "God is in Thee, and "Thou art God," he sets forth Two who were God: (in the former expression in Thee, he means) in Christ, and (in the other he means) the Holy Ghost. That is a still grander statement which you will find expressly made in the Gospel: "In the beginning was the Word, and the Word was with God, and the Word was God."142 There was One "who was," and there was another "with whom" He was. But I find in Scripture the name Lord also applied to them Both: "The Lord said unto my Lord, Sit Thou on my right hand."143 And Isaiah says this: "Lord, who hath believed our report, and to whom is the arm of the Lord revealed? "144 Now he would most certainly have said Thine Arm, if he had not wished us to understand that the Father is Lord, and the Son also is Lord. A much more ancient testimony we have also in Genesis: "Then the Lord rained upon Sodom and upon Gomorrah brimstone and fire from the Lord out of heaven."145 Now, either deny that this is Scripture; or else (let me ask) what sort of man you are, that you do not think words ought to be taken and understood in the sense in which they are written, especially when they are not expressed in allegories and parables, but in determinate and simple declarations?
However, if you persist in pushing your views further, I shall find means of answering you with greater stringency, and of meeting you with the exclamation of the Lord Himself, so as to challenge you with the question, What is your inquiry and reasoning about that? You have Him exclaiming in the midst of His passion: "My God, my God, why hast Thou forsaken me? "420 Either, then, the Son suffered, being "forsaken" by the Father, and the Father consequently suffered nothing, inasmuch as He forsook the Son; or else, if it was the Father who suffered, then to what God was it that He addressed His cry? But this was the voice of flesh and soul, that is to say, of man-not of the Word and Spirit, that is to say, not of God; and it was uttered so as to prove the impassibility of God, who "forsook" His Son, so far as He handed over His human substance to the suffering of death. This verity the apostle also perceived, when he writes to this effect: "If the Father spared not His own Son."421 This did Isaiah before him likewise perceive, when he declared: "And the Lord hath delivered Him up for our offences."422 In this manner He "forsook" Him, in not sparing Him; "forsook" Him, in delivering Him up. In all other respects the Father did not forsake the Son, for it was into His Father's hands that the Son commended His spirit.423 Indeed, after so commending it, He instantly died; and as the Spirit424 remained with the flesh, the flesh cannot undergo the full extent of death, i.e., in corruption and decay. For the Son, therefore, to die, amounted to His being forsaken by the Father. The Son, then, both dies and rises again, according to the Scriptures.425 It is the Son, too, who ascends to the heights of heaven,426 and also descends to the inner parts of the earth.427 "He sitteth at the Father's right hand "428 -not the Father at His own. He is seen by Stephen, at his martyrdom by stoning, still sitting at the right hand of God429 where He will continue to sit, until the Father shall make His enemies His footstool.430 He will come again on the clouds of heaven, just as He appeared when He ascended into heaven.431 Meanwhile He has received from the Father the promised gift, and has shed it forth, even the Holy Spirit-the Third Name in the Godhead, and the Third Degree of the Divine Majesty; the Declarer of the One Monarchy of God, but at the same time the Interpreter of the Economy, to every one who hears and receives the words of the new prophecy;432 and "the Leader into all truth,"433 such as is in the Father, and the Son, and the Holy Ghost, according to the mystery of the doctrine of Christ.