I hear a lot of Jews saying Christians believe their religion is replaced by Christianity, but this is not true. Replacement theory is just the most widely spread theory. Why? Well, because the dumbest tend to be the loudest of a group, and so, the group is labelled by what the loudest say. Crazy non-Catholic Christians are the ones who came up with the replacement theory, and given that they spread their beliefs with almost the same energy that gay activists spread their pride and joy, Christianity is labelled a religion that hates sex, Jews, women, children, science, reason, law, truth, grace, and non-Catholic faiths. And I admit that Catholics can be just as bad as those few crazy non-Catholic Christians.
But just as we cannot judge all non-Catholic Christians by those few crazy ones, so too we cannot judge the Catholic Church - nor all of Christianity - by some bad Catholics. The Catholic Church, despite what her enemies say, is the Church of Christ, and the Church believes the Lord, Jesus Christ, did not replace the Law of Moses but fulfilled it. Just as He Himself said. Christianity is Judaism fulfilled: from the Sacraments to the Scriptures to the Magisterium, Christianity is the fulfillment of what God had from the beginning planned for His People. This fulfillment dose not mean Jews aren’t loved by God anymore, for the Lord still calls them to Himself, He still leads them by ways known only to Him to Heaven.
The Ancient Covenant has become obsolete because God prophesized that, when the Messiah comes, all sacrifices would cease, save the thanksgiving offering, and so there would be a New Covenant, which, in light of the prophesy that, when the Messiah comes all the world would be saved, would be not with the Jews only but with the whole world. (Feel free to verify the prophecies for yourself) Some Jews do not believe that Jesus is the Messiah, and so, they have been cursed: not in the sense that God has abandoned them, nor in the sense that God hates them or pours His wrath upon them, and not even in the sense that they no longer worship the Lord, but in the sense that their hardness of heart has made them blind to the truth of who Jesus is.