Jobar,
Regarding a precedent for looking at the Pauline letters as composite, Albert Schweitzer had written about the efforts of Allard Pierson, Samuel Adrianus Naber & Arthur Tappan Pierson,
Verisimilia: laceram conditionem Novi Testamenti (1886):
[123]BAUER REDIVIVUS
In a critical introduction to his study of the Sermon on the Mount, Allard Pierson examined the earliest witnesses for the existence of Christianity, and in doing so threw out the question whether the historicity of the main Pauline epistles was so completely raised above all doubt that they could be treated with perfect confidence as archives from the earliest period of the new faith. (123n2)
In the year 1886 he published, in association with the philological scholar, Samuel Adrian Naber, the Verisimilia. The book was not adapted to make a deep impression. It was too much the ingenious essay for that.
The two friends combined their efforts in order to show New Testament exegetes how much they had left unexplained in the Epistles to the Thessalonians, Galatians, Corinthians, and Romans, and how many problems, incoherencies, and contradictions appear when one reads these writings with an open mind. (123n3)
[124]
But instead of making a thorough examination of the problems and laboriously arguing the case with the other students of Paulinism, the authors at once proceed to suggest what appears to them a possible solution. They claim to have discovered that the inconsistencies are due in the main to the presence of two strata of thought which have been worked together. The one is of a sharply anti-Jewish character; the other consists of milder and more conciliatory ideas.
If it be assumed, so runs their argument, that Christianity was in its real origin a Jewish sect which had liberal ideas in regard to the law and directed its expectation towards the Messiah, the antinomian sections of the Epistles represent documents of that period.
The present form of the letters is due to the fact that a later "Churchman" — the authors call him Paulus episcopus, and think that he may have served as model for the Paul of Acts — worked into them the second, milder set of ideas.
123n2) Allard Pierson, De Bergrede en andere synoptische Fragmenten, 1878, 260 pp.; on Paul, 98-112. With his doubt of the Epistles the author associates a doubt of the Gospels, and asks whether Christianity as they represent it can have been founded by a historical Jesus.
123n3) A. Pierson and S. A. Naber, Verisimilia. Laceram conditionem Novi Testamenti exemplis illustrarunt et ab origine repetierunt, 1886, 295 pp. The work gives a running analysis of the letters in the course of which very interesting questions are thrown out. Why is nothing said about the earthly life of Jesus? Why is no trace of the influence of this Paul's thought to be found in history? Do the various characteristics and actions of his which are recorded show us a character which is at all intelligible? The authors assume that the Jewish movement which led up to "Christianity" at first had only to do with the Messianic belief in general. Only later, through the blending of Greek myths with Isaiah 53., did the belief arise that the expected Messiah had already come and had passed through death and resurrection. The analysis of the Pauline Epistles is followed by essays upon the Paul of Acts and some chapters on the Fourth Gospel. The close is formed by an essay on the gradual origin of the conception of Christ in the New Testament.
[Paul and His Interpreters: A Critical History (1912)]
Their take on how the letters came to be as we receive them, was almost the polar opposite to what I have concluded, but I think I can justify my POV with a milder set of ideas being overwritten with "liberal ideas in regard to the law and directed its expectation towards the Messiah, the antinomian sections" which were peculiar to the evolved Christ movement.
For me there were two players here:
1) A Jesus movement centered on the inauguration of a fruitful age to be enjoyed by descendants of Abraham, with concentration on its anointed leader.
a) Jesus, was assumed by many to have been this leader. After his execution, though, the belief arose that God will resurrect him one day to inaugurate the new blessed age. This was led by members of Jesus' family, so the family likely laid claim to Judean crown. They were competing with Herodians, and may have been a rump faction within the Hasmonean dynasty.
b) One faction within this movement, consisting of gentiles who have converted to Judaism, apparently hoping to participate in this fruitful age to come along with natural born Judeans. The Judean rebellion of 66-73 CE changed this faction into bitter enemies of the Judean people who participated in the revolt. Not willing to believe that they were wrong about God letting them participate in the fruitful future age, they developed the concept of their dead leader Jesus actually being a semi-divine redeemer, "Christ," fashioned from Platonic cosmology as understood by Philo, and proto-gnostic concepts developed by Judean's who had lost faith in their national God in consequence of that war.
2) A completely unrelated Paul movement centered around members of a large Herodian household with estates throughout the Mediterranean region. Paul, a retainer, and perhaps son, of a gentile convert to Judaism, his father probably having been manumitted by the master of the household, when he first encountered gentile slaves and retainers of this household who wished to be included in the future blessed age all Judeans hoped for one day, was hostile to any attempt by them to evade full conversion to Judaism and adherence to circumcision and law observance, like his dad had. In time, he had his seizure which he interpreted as a vision which caused him to see a solution for treating these "faithful" gentiles as justified before God, by means of the same simple faith that Abraham had that God would fulfill his promise of that fruitful inheritance, as Abraham was thus justified before his God even before he had himself circumcised and well before there was any Law, making them "spiritual" children. It was creative, but not popular. He suffered a lot of blow back from other Judeans who were not so lenient. After his death, the remnants of this movement was decimated by the aftermath of the Judean rebellion, where the status of Herodians was degraded as Judea was no longer a state in Roman preservation to be handed over to a strong Judean prince when it would be convenient for the Romans.
I think the Jesus movement, now developed into a mystery cult around a semi-divine redeemer, reached out to their former foes, the Herodians, by adopting these letters of Paul with their peculiar solution to the justification of gentiles, and adapted them to make Paul a Christian. The result of all these digressions, glosses and redirections was clunky and doesn't read smoothly. But it contained seminal elements of the Christ theology that was developing. Finally, the author of Hebrews, who was actually a very thoughtful person, worked out the Christ theology of the letters, which is rough and tumble, into a coherent theology of Jesus as the divine redeemer Christ.
<puf puf> That was a lot to get out in one breath!
DCH