It must have been difficult in the early days of the Church. Jesus was a Jew, the early church started from a group of Jews, but Christianity was a very different thing. Paul was also a Jew, and a well-read scholar. In helping the early church understand what the role of Jews and non-Jews was, he somewhat cuts to the chase: God made the Jews the people of the promise that is fulfilled in Jesus. Now, with Jesus as the head of the church, we are all part of the fulfillment of the old promise and the hope of the new one.