Opening the gospel to Gentiles as well as Jews wasn’t easy: there was some Jewish believers who still thought the new Gentile believers should observe the Law. Peter’s vision and Paul’s evangelising hadn’t been enough.
So Paul wrote to explain:
Galatians 3:24-25 Let me put it another way. The law was our guardian until Christ came; it protected us until we could be made right with God through faith. And now that the way of faith has come, we no longer need the law as our guardian.
There was no need for Gentiles to become Jews to become believers:
Galatians 3:18-29 There is no longer Jew or Gentile, slave or free, male and female. For you are all one in Christ Jesus. And now that you belong to Christ, you are the true children of Abraham. You are his heirs, and God’s promise to Abraham belongs to you.