See Religions and Expectations. Poul Anderson describes a society in religious ferment where new beliefs can arise, coalesce and solidify into dogmas. Jaan the Shoemaker believes not that he is the incarnation or reincarnation of a god but that his consciousness has merged with that of an Ancient. In this science fictional, future historical context, Anderson has reproduced past historical turning points.
-Frances Young, Chapter 5, "Two Roots or a Tangled Mass?" IN John Hick, Ed, The Myth Of God Incarnate (London, 1977), pp. 87-119 AT p. 98.
(Addendum: But Young goes on to show Jewish antecedents of incarnational theology.)
(i) Jesus was able to be the Messiah promised to the Jews because he was in patrilineal descent from Abraham.
(ii) He was not in patrilineal descent from Abraham but was the Son of God because the divine Spirit had impregnated his mother.
(iii) He was not only the Son Of God but also God the Son because, although this was not known before, God is three Persons and Jesus was the Incarnation of the Second Person.
(iv) He was the Incarnation not of a divine Person but of a lesser, although powerful, supernatural being.
Paul started with (i), then, under the pressure of controversy with Samaritan Gnostics, adopted (iv) but did not preach (ii) or (ii). The Trinity doctrine is not in the New Testament but is inferred from John's deification of the Son and personification of the Spirit. Also of interest are three entirely different accounts of Jesus' last words before his death.
Addendum: I have tried to clarify the developing doctrines about Christ here.