https://www.btstories.com/letter-to-the-galations/

Teachers from Jerusalem went to the church in Antioch and taught that Gentiles had to obey the Laws of Moses in order to be totally forgiven from their sins. After the Christians in Antioch rejected this doctrine, those same teachers went to Galatia, to the churches Paul and Barnabas had started during their first missionary journey. Paul found out that the Christians in Galatia were accepting this teaching, so he wrote a letter to them explaining their freedom in Christ.