Remember that during the second and third centuries, the OT was very much neglected and the concentration of the Church was on the message of Christianity, not its divergence from Judaism.
When I was originally faced with this prospect, I was appalled, even angry. But evidence is too compelling which is why it is so well filtered by the Church. When was the last time you had a rabbi give a sermon on how the Jews see the Passover Lamb and what the Christians innovated from it? Jews are considered perfidious (unbelieving) "apostates" and all their views are heretical (kettle calling the pot black) and labeled.
Christianity is not Judaism, which was made clear in the Gospels and even clearer in Acts and the epistles. Why were you angry? Was the Torah rewritten? The rest of the Tanakh? What changes were made in the translation of the Septuagint - inadvertently and deliberately? We have some evidence, as we have evidence of the NT massaging.
I believe that the changes were required because of the inability of man to properly understand God, so we view Him, as we do everything else - through our anthropomorphic and current societal filters. I have no proof - but I do believe that this is what happened, just as I believe that the bishops converged in their meeting room in Nicea were led by the Holy Spirit to make the decisions that they made. Same as the cardinals in the Vatican when they are shoveled into the Sistine Chapel and told to stay put until a new bishop is chosen.
I have no proof except for the longevity of the practice and the fact that it makes sense to me on an experiential basis, as well as a theological one.
The OT was neglected at first because it was believed, by some (such as Marcion) that the OT God was not the God of the risen Christ. Also, Christians were doing everything to make the Jews look like the bad guys. It was +Irenaeus who, at the end of the 2nd century, realized that without the OT Christianity had no legal appeal, and began to integrate the OT and the NT.
Christianity is not Judaism, which was made clear in the Gospels and even clearer in Acts and the epistles. Why were you angry?
I was angry, as a believer, that my Church had to resort to corruption and manipulation in order to establish what it claimed to be the true dogma. The Gospels, actually affirm Jesus' teaching as Judaism which, unless it was written from ignorance by non Jews, seem rather deceptive. The first defection from Judaism is Paul's antinomialism.
I believe that the changes were required because of the inability of man to properly understand God
Mark, the changes were required to create an a whole new religion using Judaism as its legal authority pretty much the way Mormonism was created.
Was the Torah rewritten?
No, some of the changes are quite subtle. A good example of manipulation of scriptures are found in such instances as when the suffering servant is said to suffer for our iniquities instead of the Tanakh's from our iniquities.
Other issues revolve around the idea of sprinkling of the blood of the innocent victim atoning for our sins. Jewish customs required animal sacrifice only for things committed inadvertently (unintentionally), and in no instance did it ever involved sacrificing a human being, especially a Jew.
For intentional sins, the OT is very clear that no man (or animal) can atone for, except the person who committed them. And that he can do only by repentance and prayer. So, Christian teaching that Jesus was like a sacrificial animal whose blood atoned for the sins of the world is alien to Judaism, yet it is presented by Christians as being part of it. Furthermore, the blood had to be sprinkled on the altar in the Temple.
Another example is the idea that Jesus was like the Passover Lamb. The blood of the Passover Lamb was not shed to atone for anyone's sins, but to show the Egyptians that their god (they worshiped lambs the way Indians worship sacred cows) is no god; it was an act of desecration of an Egyptian deity demanded by God of Israel. Equating Jesus with the Passover Lamb is to the Jews like saying Jesus was a false god. But the Christians weaved a different story around that story.
This is no different than the Mormons saying their trinity is one god in purpose and not in nature. It is a complete distortion of the core Christian dogma used to create a new religion.
Now, I am not interested in challenging your beliefs, Mark. I merely state what I know And I know the Church never told me the whole truth and nothing but the truth. Instead, it seems it fabricated its own truth and I think I can see pretty clearly why it took it 300 years to cook that stew.