This research yielded some surprising results.
1) As we know it today, Judaism is only about 1500 years old. To be sure, Rabbinical Judaism uses the Hebrew Bible as one of its principle sources of inspiration, though it is in no way identical with the religion documented there. The most important innovation is the idea that their are two Torahs, the written and the oral. The latter, whose contents are known only to the rabbis, provides many precepts not stated in the written Torah. For their own part. Christianity and Islam make much use of the Hebrew Bible without being identical with the earlier faith.
2) In this light it would be most accurate to speak of four Abrahamic religions, not three. Yet the faith of ancient Israel is extinct, leaving (Rabbinic) Judaism, Christianity, and Islam as the three living specimens.
3) It follows that Christianity is not the daughter of Judaism; rather, if anything, the relations are reversed, since Christianity arose about 400 years earlier.
4) Like its precursor, known to us from the Hebrew Bible, Judaism harbors a number of polytheistic elements.
5) In Christianity, the doctrine of the Holy Trinity is effectively polytheistic.
6) In Christianity, Trinitarianism was actually the second stage, the culmination of a more complicated development, being preceded by binitarianism, the doctrine that only God the Father and Jesus Christ were divine. Nothing in the New Testament requires us to accept that the Holy Spirit was the third, coequal partner in the firm.
Now comes an important new book, shedding light on all these questions. It is The Jewish Jesus: How Judaism an Christianity Shaped Each Other, by Peter Schäfer, who is Professor of Jewish Studies at Princeton University. The title of this book would suggest that it is yet another monograph affirming the truism that Jesus was a Jew, standing alongside other books of this genre by John Dominic Crossan, E. P. Saunders, and especially Geza Vermes.
There is no need to turn to these books to acknowledge the following points, easily derivable from the four canonical Christian Gospels. From his birth Jesus was raised a Jew. He was circumcised on the eighth day (Luke 2.21) and bore a common Jewish name, Yeshua, "he [God] saves" (Matthew 1.21). In fact, scholars have determined that Yeshua was the fifth most common male Jewish name of the time. Joseph was the second most common male name and Mary the most common among women. The child Jesus was presented to the Lord in the Jerusalem temple (Luke 2.22; cf. Deuteronomy 18.4; Exodus 13.2,12,15), A sacrifice was offered for him, a pair of doves and 2 young pigeons, indicating that his family were not wealthy (Leviticus 12.2,6,8; Luke 2.22-24). Thus Jesus was raised according to the law (Luke 2.39).
These points being granted, it should be noted that Jesus belonged to pre-Rabbinical Judaism, differing in many respects from the faith that came to fruition in the two Talmuds (where he is sometimes denounced, as Schäfer showed in another monograph). One must be careful of anachronism.
Evidently, The Jewish Jesus essentially replicates the author’s German original, which I have not seen. In translation the title of that book is “The Birth of Judaism from the Spirit of Christianity.” This sounds very much like my point no. 3 above, with Christianity being primary and Rabbinic Judaism coming after. At all events, in this version Schäfer prefers a more interactive model in which a number of ideas circulated freely among both parties.
The conventional view of the contrast between Judaism and Christianity is that the one is strictly monotheistic, the other tritheistic. With regard to antiquity, especially late antiquity, Peter Schäfer assembles considerable evidence to undermine this view, exploring a whole range of partner-deities for the supposedly unique God of the Jewish tradition. These motifs include the duality of Elohim (literally “gods”) and Yahweh in the Pentateuch; the contrast of the old god (the “ancient of days”) and the young god; the use of plural verbs in the Hebrew bible to describe divine actions; the curious figure of Metatron, ostensibly the chief of the angels; and the idea of the eternal David.
All of these nominations point in the direction of binitarianism, the idea that there are two high gods. This notion finds a parallel in gnosticism, but Schäfer thinks that this is not very important, as in that tradition the partner tends to have a negative connotation.
In fact, Schäfer showcases the binitarian concept. Here Judaism, or at least some strands of it, joins with New Testament Christianity, which was basically binitarian (with the Holy Spirit not yet admitted to full partnership), Thus Judaism was not strictly monotheistic, nor was Christianity always strictly trinitarian. Schäfer holds that binitarianism found an important support in the imperial concept, developed by Diocletian at the end of the third century CE, of the Augustus (or chief emperor) assisted by the Caesar (or junior emperor).
This book, by a major scholar in the field, is carefully composed. I recommend it highly.