Furthermore, it just seemed quite offensive to Jewish people to tell them that nope, the system you were, according to the Bible, given by God wasn't sufficient after all. As I did not know any Jews who became Christians, it seemed a non-issue in the Christian church to routinely misinterpret the Jewish faith and misrepresent it to shore up doctrine.
The more I learned about Judaism, the less sense much of the doctrine made, and the more offensive some of the assumptions became.
I've become somewhat more sensitive to Jewish sentiments about Christianity in the last two or so years, particularly because I've started taking an interest into how Judaism sees Christianity.
Christians have, for quite a long time, thought only of how Christianity might have value for Judaism, rather than the other way round: how Judaism might have value for Christianity.
I think if we actually investigated the matter further, we'd find that Judaism gives Christianity more credit than we may initially think, but not in the way that many Christians would expect (or would like), particularly if you think in evangelistic terms. The credit is more about acknowledging Christianity's legacy in possibly bringing the world's people into a relationship with the Abrahamic God, not expressing an interest in conversion.
Consider, for example, the Noahide movement and the notion of Noahidism. Christians in theory can qualify for being Noahides. One problem, however, is the doctrine of the Trinity that is upheld in many Christian groups.
Jesus' sacrifice was a continuation of the old notion that "the law requires that nearly everything be cleansed with blood, and without the shedding of blood there is no forgiveness." However, an important difference is that Jesus' sacrifice is to be seen as once and for all, thus facilitating atonement even for sins not yet committed: "Christ was sacrificed once to take away the sins of many people."
Jesus' sacrifice is portrayed as being an improvement on the old sacrificial modalities which were considered externalistic and superficial: "the gifts and sacrifices being offered were not able to clear the conscience of the worshiper. They are only a matter of food and drink and various ceremonial washings—external regulations applying until the time of the new order."
Hebrews goes into substantial detail on how Jesus' sacrifice was different.
The idea of the "atoning sacrifice" or "martyr-crucifixion" has many facets to it. The atoning sacrifice theory is not the only theory Paul offers. The other is the Law-nailed-to-the-cross theory which you will find in Colossians 2:14-15.
He forgave us all our sins, having cancelled the written code, with its regulations, that was against us and that stood opposed to us; he took it away, nailing it to the cross. And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross. Colossians 2:14-15
By "written code," Paul implied that it was legalistic sentiments that had Jesus arrested, condemned and sentenced to death. Legalistic ideology condemned an innocent man, so legalistic ideology lost its authority. This was what freed us from legalistic ideology.
The replacement theology that promotes the idea that Judaism was "dumped" by God after the crucifixion assumes that Judaism was legalistic by nature, rather than legalistic sentiments just being an approach some people had to Judaism. The idea, however, that Judaism was legalistic even at that time is debatable.
Here are some sites debating or disputing the assumption that Judaism was legalistic in the first century:
What was Judaism like?
Paul and the Law
Evaluating the New Perspective on Paul
Cornelis P
(BTW, I haven't gone very far in reading the above articles, and this post was written largely in ignorance of the points made in them.)
Paul's efforts to convince those with legalistic sentiments of his new theology where he discarded these legalisms can be found in quite a few places in his epistles. A notable example is that of circumcision. Paul's ideas on legalism have given a lot of Christians the view that Judaism is legalistic.
But the question is, why should a document written in the first century be used to determine whether a religion is of legalistic nature? Do "religions" not "change" and "evolve" over time to adapt to cultural idiosyncrasies? Moreover, can a whole religion be legalistic? I think not. I think Paul was speaking of a subset of Judaism, particularly those with a legalistic mindset. Just like Christianity has fundamentalists today, Judaism too, had its fundamentalists.
Fast forward 2,000 years and you find Christianity itself has often been quite legalistic, particularly in its approach to theology. In much the same way that Judaism suffered from legalistic sentiments in the interpretation of the Law, Christianity has suffered from legalistic sentiments in the interpretation of its own theology.
Just as Paul argued against "physical circumcision" being mandatory, I could argue against the idea that it is mandatory to believe in the Biblical Inerrancy Doctrine, Trinity doctrine, replacement theory doctrine, pre- and post-millenialism, Jesus being God idea, etc.
I think what Paul proposed was fairly radical. Many modern Jewish scholars have suggested that Christianity was much like an early Noahide movement. Christianity is the first major religion that took an active role in promoting the idea of the "Righteous Gentile" being an equal to a Jew. Some of the rules made up for Gentile Christians are much like the Seven Noahide Laws.
But Paul went further than the Jews of today in their support for the modern Noahide movement. He believed he could do away with distinctions between Jews and Gentiles altogether. Even today, Jews keep their distinctions from Noahides.
I think Paul was getting a bit too ahead of himself. I think he was in some ways too optimistic. Prematurely optimistic. He was trying to change things way too quickly. He was promoting the idea that Jews could just give up their Jewish identity. He did it at a time when this new "Noahide" movement which we now call Christianity was only just getting on its feet.
He didn't know the world was round. He, like most other ancients, thought the world was flat. He didn't know the world was that big. He didn't know of a world much beyond the Mediterranean. He didn't know how much work still need to be done. So much for romantics and idealists.
One thing that replacement theology assumes is that God "dumped" Judaism and that it therefore became useless. This, however, assumes that theology is more important than socio-political legacy. Many of the things Jesus did were social and political in purpose, nature and consequence. Even the crucifixion can be said to be socio-political. I see the socio-political as more important than theology because theology is largely theoretical and imaginary whereas socio-political legacy has sentimental value and can have an impact on whole communities and their collective psyches.
To think that Judaism just becomes obsolete just because of a theological theory is just ridiculous IMAO.
The question of usefulness in our relationship with the Abrahamic God is not limited to theology, but includes the social and political. The value of Christianity and its Jesus Legend does not rest solely in theology and nor is it so for Judaism.
Given that Judaism can have value socially and politically in our pursuit of the Abrahamic God, if it does offer something of value socially and politically for adherents of the Abrahamic faiths, it's something we can't ignore. I see the emerging Noahide movement as one such example. If Christians qualify as Noahides and can be included in the Noahidic collective, this is significant. Judaism is far from being useless. Moreover, if Christianity was an early Noahide movement, the idea isn't so incompatible to Christianity. It's quite reasonable and acceptable.
