In terms of “replacement” I think that’s a complicated theological question. Christians will generally fall into one of two buckets.

All Christians believe that the Christian church is a new universal covenant from the God of the Hebrew Bible.

Some Christians believe that the Church has fully replaced the covenant that God established with the Jewish people. Others believe that there are now two covenants, one with the Christian Church, the other with the Jewish people.

Regardless of the beliefs in either of those two positions, there really is no way to believe in the New Testament without believing that Jesus was the Jewish Messiah and that Christianity is God’s plan for the world. Believing in that is what makes someone Christian.