Margaret Barker's book has, as its core thesis, a concept so heretical that it almost goes full circle and comes back to being 'sound' again. I find the theory fascinating, and reasonably convincing.
It is fairly widely known and agreed by scholars that much of what we call the Old Testament was compiled and edited around about the time of the return from the Babylonian exile, that is to say a little longer ago than 500 BC.
Barker's central thesis is that during this time of compiling, the 'redactor' who compiled the work rewrote or selectively edited significant portions of the text to give a very biased account. Her specific main claim is that the pre-exilic religion of Israel had not been monotheistic at all, but had worshiped at least two gods, but this fact was written out of history by the (monotheistic) redactor, although vestiges remain in the writings.
Very broadly speaking, she says, before this the temple worship was directed to Elyon, the 'Most High God' and to his son Yahweh, who went by a number of names and was understood by some to have both male and female aspects, resulting in the female personification of Ashera/Wisdom.
Erm, so the theory is that there was an ancient religion with a Heavenly Father, an incarnated Son and a less well defined third persona linked to wisdom. Does that sound at all familiar?
Barker, by drawing on the books of the OT and a lot of extra-canonical writings, both from the OT and NT eras, does a fairly convincing job of demonstrating that her thesis is at least worthy of serious consideration, even if she doesn't necessarily manage to prove anything.
I'll admit I got a bit lost in her explanations of how the female persona of Wisdom was understood to be a second aspect of the second God, but I find her evidence that the pre-exilic religion worshiped both the 'Most High' God and Yahweh as discrete and distinct gods as compelling and even convincing.
Why is it heretical - from a Christian viewpoint - to claim that the Jews misunderstood the nature of their God and mis-represent God in the OT? We believe that the Father God and Jesus His Son are discrete and distinguishable persons, and that the Jews are wrong in believing otherwise. What if they once had the right belief and rejected (or lost) it in favour of monotheism? Is it just because their (wrong) belief got incorporated in our Bible that we can't consider that maybe they knew the right stuff and then rejected it?
Barker claims (and provides evidence) that while the monotheism of the redactor is the dominant belief of the written texts (at least, the canonical ones) from the OT era, that the 'common people' (i.e. those who were never carried away to exile) continued to worship the plural Gods long after the exiles returned. Indeed, when Philo was writing 500 years later, there is clear evidence of a plurality of Gods in his (just pre-Christian) writings. He even uses the word 'Logos' to refer to the second God, something that the writer of the 4th gospel would use for Jesus 50 years or so later.
What she suggests (but does not explicitly say in this book, I believe this is the core of her other book 'The Older Testament) is that, basically, the ruling class of Judah/Israel was removed to Babylon and indoctrinated out of their pluralistic belief into a monotheistic one, and then they were returned to Judea to impose the same beliefs on the common people. But the common people never really lost these beliefs, only those who were the recorders of history lost them. So when, several centuries later, Jesus comes along claiming to be the 'Son of God', the common people understood this, and exactly who he was claiming to be. However the priests and rulers, who had long abandoned the pluralistic beliefs, were the ones who rejected Jesus.
The book bombards the reader with evidence. To be honest, I'd have been just as convinced if about half of the stuff was removed - the chapter covering the writings of the gnostics, for example, was more confusing to me than revealing, as were some of the other chapters on "The Name" and the non-canonical 'Wisdom' writings.
However, the final two chapters (where she addresses the writings of the early Christians and the books of the New Testament) are probably the best demonstration of her thesis. Reading the final chapter is an ongoing 'why had I never noticed that before' revelation to the reader and more than convincingly demonstrates that, whatever else the early Christians believed about Jesus, they equated him (God the Son) with Yahweh (the God of Israel in the OT). This is demonstrated by comparing numerous NT passages about Jesus with OT equivalents about Yahweh. Its not that they saw Jesus as being like Yahweh, it is clear that they saw him as being Yahweh.
So even if the reader is not convinced by the other evidence (although I am, reasonably) then you still are faced with the final conundrum. If the first Christians believed Jesus to be Yahweh, and were taught by Jesus to pray to His Father, then who is the Father? The Father cannot be Yahweh, as he is the Son. Ancient traditions, although obscured in the OT, still clearly make reference to the Father of the gods, the Most High God. This is the Father of Jesus.
All this will make me read both Old and New Testaments in a new light...