Why do you think Paul, in the book of Galatians especially, was so bitterly opposed to fellow Jewish Christians who sincerely believed that Jesus wanted people to continue to honor and obey the Jewish laws that God gave them through Moses? After all, Jesus himself had probably observed them throughout his life.
Paul taught that Jesus changed everything, and that the agreement God had with the Jewish people had expired and was replaced with a new agreement with all people.
Bible experts refer to those agreements as the old covenant (based on obedience to Jewish laws in the Old Testament) and the new covenant (based on faith in Jesus and guidance from the Holy Spirit who writes God’s laws on each person’s heart).
Paul seemed to know that if his opponents won the argument, Christianity would simply have become one more group in the Jewish religion. There would be Pharisees, Sadducees, and Christians. And they would all be Jews who felt obligated to observe all the ancient Jewish laws.
But Jesus told Paul that it was time to bring the non-Jews into God’s family. The Lord said about Paul, “I’m giving him the job of taking my teachings to non-Jews, kings, and Jews alike” (Acts 9:15).
Excerpt from Leader’s Guide & Atlas for Galatians