"...the notion that the faith of the Prophets and Moses is the same faith we have -- an assertion that Moses and the Prophets would have recognized Christ as God. I believe that is what Agrarian had said, and if I am misrepresenting it I am pinging him for a correction."
Yes, you basically have it right. I would choose to clarify it by making sure that it is clear that I do not believe that Abraham could recite the Nicene Creed or that Moses, had he been asked while he was alive, would have said that God would be born of a virgin, become man, and walk among us. There was a gradual revelation throughout the Old Testament, and a very big revelation that changed everything in the Incarnation.
There have been unquestionable developments all along -- the worship and faith of Abraham is more developed and reflects more "refinement," if you will, than did that of Noah. The tabernacle worship instituted by God through Moses was more developed than was that of Abraham. The temple worship that began under Solomon again was more developed. With each writing of each prophet, God was further revealing Himself to his people. At each step along the way there were those amongst the chosen people who recognized this revelation and believed it, and those who killed the prophets.
Synagogue worshiop developed in circumstances of exile and amongst those far from the temple, and developed as a separate type of worship and prayer alongside of and complementary to the sacramental temple worship. Orthodox Christian worship is a continuation of both synagogue and temple worship, and it, too, has developed over the centuries.
I would certainly maintain that throughout the entire process, it is the same God being worshiped and that the core faith of the faith never changed, and you are correct that I have said (agreeing that it is an "unprovable" speculation) that Moses and the Prophets would have recognized Christ as Messiah and accepted him as God, recognizing that he was the same God who had revealed himself to them.
The main "evidence" for this comes from what Christ and the Apostles said in the NT, such as: "Do not think that I will accuse you to the Father: there is one that accuseth you, even Moses, in whom ye trust. For had ye believed Moses, ye would have believed me; for he wrote of me. But if ye believe not his writings, how shall ye believe my words?"
That said, I hasten to add that your objection to this self-understanding of the Church is a legitimate intellectual position -- one that I don't think could ever be "disproven" through argumentation or evidence.