How can the Church teach for 2000 years that everyone, Jews included, must convert to the Church in order to be saved, and now today acts as if the Jews have a valid covenant with God?
It is very evident from scripture and tradition that Jews must convert for salvation.
God called Abraham to be the father of a nation that would lead to the salvation of all nations. God’s promises to this faithful man and his children is the covenant that St. Paul made reference to when he wrote:
In respect to their election [by God], they [the Jews] are beloved because of the patriarchs. For the gifts and the call of God are irrevocable.–Romans 11:28-29.
It is on the basis of this covenant with Abraham that the Gentiles can be saved via Christ because:
Scripture, which saw in advance that God would justify the Gentiles by faith, foretold the good news to Abraham, saying, “Through you shall all the nations be blessed.”–Galatians 3:8.
This covenant which saves Gentiles through Christ makes Gentiles part of the holy nation of Israel–the New Israel. As it is written:
You [Gentiles] were cut from what is by nature a wild olive tree [nations not in a covenant relationship with God], and grafted, contrary to nature, into a cultivated one [the nation of Israel].–Romans 11:24.
And:
You do not support the root [the Patriarchs and the Jews who first accepted Christ]; the root supports you [Gentiles].–Romans 11:18.
This doesn’t mean that Christ plays no part in the salvation of Israel. Exactly how this happens is yet to be seen. But this does not negate the covenant that now saves Gentiles through Christ, because if the covenant of promise to Abraham is no longer in effect you who are Gentile believers inherit nothing.
For to the Jews “belong the adoption, the glory, the covenants, the giving of the law, the worship, and the promises…and from them, according to the flesh, comes the Messiah.” (Romans 9:4-5)
Again if the covenant is not in effect your share in the promises is no share at all. But this is not so for the reason you can count on this is that “God has not rejected his people whom he foreknew.”–Romans 11:2.
The Church teaches that Christ is the Savior of the world, of you and me, Gentile and Jew: “All have sinned and are deprived of the glory of God. They are justified freely by his grace through the redemption in Christ Jesus.”–Romans 3:23-24.
What you may be thinking about is the Mosaic Law covenant. It is not binding on any Christian, Jew or Gentile. But that is not the same as the covenant between Abraham and his children who now include all nations. That is still in effect.
The promise may be guaranteed to all his descendants, not to those who only adhere to the law but to those who follow the faith of Abraham, who is the father of all of us as it is written, “I have made you father of many nations.”–Romans 4:16, 17.