I picked up a brief book by Daniel Boyarin titled The Jewish Gospels. I am about a little under halfway through and find it engaging. Boyarin points out that post-exilic, pre-rabbinic Judaism was complex. There was not a single Judaism but a variety of Judaisms. Boyarin highlights this when he says:
. . . [T]here were many Jews both in Palestine and outside of it, in places such a Alexandria in Egypt, who had very different ideas about what being a good, devout Jew meant. Some believed that in order to be a kosher Jew you had to believe in a single divine figure and any other belief was simply idol worship. Others believed that God had a divine deputy or emissary or even son, exalted above all the angels, who functioned as an intermediary between God and the world in creation, revelation, and redemption. . . . Thus the basic underlying thoughts from which . . . the Trinity . . . grew are there in the very world into which Jesus was born and in which he was first written about in the Gospels of Mark and John. (Daniel Boyarin, The Jewish Gospels: The Story of the Jewish Christ [New York: The New Press, 2012], 5–6)
The idea of the Trinity then is not, as some have argued, something that is foreign to the thought of the biblical writers. Sure, the creedal formulations of the fourth and subsequent centuries have a more Greco-philosophical feel to them but the content that they express are biblical and not un-Jewish.
To take it a step further, the two contrasting groups that Boyarin mentions are likely similar to those in the historical situation that Paul N. Anderson finds in 1 John 2:18–25. This passage describes two sets of antichrists: strict monotheists Jewish Christians and docetists. Applicable to this discussion is the first set that sought to revert back to a strict version of monotheistic Judaism, similar to that of the first group mentioned by Boyarin, because they claimed that the Christians who believe in the Father and the Son, the belief of Boyarin’s second group, actually believe in ditheism.
For those who would like to further pursue the subject, you may find of interest Daniel Boyarin, “The Gospel of the Memra: Jewish Binitarianism and the Prologue to John,” Harvard Theological Review 94, no. 3 (July 2001): 243–84.
You may read Paul Anderson on the antichrists in 1 John and on Revelation in Paul Anderson on Revelation — Session 1.
UPDATE: Boyarin’s “The Gospel of the Memra” is available here, courtesy of his webpage at University of California Berkeley.