This could be controversial for some or maybe even most Jews, whereas it cannot by definition be controversial for Christians. Then again, Christians will no doubt balk at the notion that Christianity brought no new ideas into the world.
Of course, we must bear in mind that that Judaism is a river with many upstream tributaries and downstream branches, streams, and eddies. In the case of Christianity, one of the branches broke off and became its own river.
Evidently, there is no "normative" Judaism. The moment someone claims to represent it, someone else will contradict him. Two rabbis, three opinions, etc.
I recently read a biography of Maimonides, who some consider to be the Greatest Genius of Judaism. Of course, others will argue with that characterization. In any event, he assembled a list of thirteen principles of the faith; number one is the existence of Number One, the Creator.
I suppose we can look at the thirteen principles as a kind of flow chart -- the flow of the above referenced river; a river of light, as it were. So we're all together at the headwaters, the source, the cosmic spring.
Number two: his unity. Oops! Here the river seems to branch in two, because Maimonides would maintain that a trinitarian God contradicts his unity.
However, I think we have to give the early Christians -- being that they were Jews -- credit for appreciating the dilemma. Of all people, they would be aware of the difficulty of squaring this circle, which took centuries to officially resolve, or to congeal into a principle, i.e., a trimorphic God with distinctions but no separation. (This primordial Three must be considered a quality, not quantity.)
But according to Boyarin, not only is such an idea kosher, but similar ideas were being discussed in Jesus' day, and indeed, centuries before. He introduces some fascinating research showing how mono-theism emerged from poly-theism, but not always in a smooth, harmonious, and seamless way. That is to say, one can at times detect unassimilated godlings hovering around the one God. (Not to mention the ongoing temptation to revert to out-and-out paganism.)
To back up a bit, the reason I find this fascinating is that it mirrors the development of the mind, which moves from fragmentation to synthesis. One can look at this quite abstractly as the basic metabolism of cognition. For reasons we won't get into, Bion symbolized the fragmentation PS, the synthesis D. Thus, one of the ground floor operations of the mind is PS↔D. Note the bi-directionality of the arrow, as things are always falling apart and reconstituting.
Aren't they? Hope it's not just me.
You could say that a "nervous breakdown" is a descent into unremitting PS. These fragments of PS are persecutory and predatory, especially as they become more primitive. Even "curiosity" is a kind of "pain," i.e., the pain of not-knowing. However, we must tolerate the pain of PS in order to await the coherence of D. Which then becomes a new pain in the PS.
So, long story short, this is how I regard the historical discovery of the one God. It is literally a discovery, because prior to that, reality is too occluded by psychic fragmentation to apprehend him. Thus, polytheism is really the residue of psychic fragmentation, the inability to intuit the whole. One-ness cannot be revealed to scatterbrains.
Interestingly, looked at this way, the trinitarian God is a kind of eternally dynamic PS↔D. I don't mean to vulgarize the deity, or contaminate him with our own limited ideas.
However, think of the idea of kenosis, i.e., the self-emptying of God. With the Incarnation, God essentially tosses his unity into our world of fragmentation and multiplicity, culminating with the Cross. Looked at this way, the Resurrection is the recovery, the re-synthesis and re-integration. Thus, in a way, Jesus' passion is the last Word in PS→D. Just when the apostles think the world is hopelessly disintegrated and flying off its hinges, it reintegrates at a higher level than they could have possibly imagined. "Transfiguration," you might say, is a very high-level D.
However, Judaism has its own version of primordial PS↔D; in fact, several versions. For example, Steinsaltz, in his Coon Classic, The Thirteen Petalled Rose, writes that "Creation itself, and the creation of man," is "a descent for the sake of ascent." Even the Sabbath can be seen as a day devoted to D after six days of frazzled PS. It is a return to the One, a reset, a reJewvenation. (Note also that the Sabbath is the telos, or purpose, of creation; or, at the very least, the opportunity to re-orient oneself to that transcendent unity.)
There is also the "shattered vessels" principle. (I just googled it and this is the first thing that comes up, so there are no doubt better explanations.) If I am not mistaken, the basic idea is that the world is shattered, scattered, battered and tattered, and that it is our task and privilege to help put it back together. Which is what we attempt here at *One* Cosmos. Yeah, someone's gotta do it.
Back to Maimonides' list: number three, denial of God's corporality. Here is another one Boyarin would dispute, or at least there were some ancient streams that thought otherwise. The question is, were those just pagan streams holding on to atavistic dreams of the godman? Or is it a legitimate principle?
Boyarin claims that Jesus is new, but the idea is very old. The only thing new is that this particular individual is the Son of Man, but Jesus did not invent the concept. Rather, again, it is in Daniel, and it is also present in the more recently discovered book of Enoch, which is roughly contemporary with the earliest Gospels. No, it is not scripture, but it does prove that the expectation of the Son of Man -- the divine in human form -- was in circulation.
Gotta go. Argue away!