Doug Mason: The first people who wrote and accepted the idea of a God-becoming-man were Jews.
Doug, I have not read, "The Jewish Gospels: The Story of the Jewish Christ," but Sydney Uni Library has a copy, and I shall look at it soon, as I am not sure about the thought, expressed in the concept, "The first people who wrote and accepted the idea of a God-becoming-man were Jews." If the author is considering the thought expressed in Genesis 18> then I understand, otherwise I would have to consider, at least in western thought, that the Greeks were first.
Robin Lane Fox discusses the concept in his "Pagans and Christians in the Mediterranean World," chapter 4, titled, "Seeing the Gods." He draws attention to the writings of Homer (Ninth or Twelfth century BCE) in his epics the Gods were not just onlookers, they became participants and, 'stand beside' their heroes, as 'evident helpers.' At the end of the Iliad, Priam (an elderly man), afraid, defenceless, sets out to go to Achilles's camp. On his journey he meets a handsome young man who became his guide. Priam explains his guide as divine assistance. "Some God has held his hand over me." The young man turns out to be Hermes.
Understanding that common and age-old belief, helps us understand the crowd response in the claimed incident in Lystra, when Paul performs a miracle,
" The gods have come down to us in human form! Barnabas they called Zeus, and Paul they called Hermes because he was the chief speaker." (Acts 14: 11,12)