It came to Paul’s attention that certain false teachers were causing problems in the church. He was disturbed that the Galatians had been seduced by a perversion of the Gospel (1:7, 3:1). These men were trying to impose circumcision and the laws of Moses on the believers even though they were Gentiles. These legalists believed that circumcision was a requirement for a person to be saved, that is, faith in Christ was not enough.
Paul denied that any legal requirement had nothing to do with the New Covenant in Jesus Christ. A person is saved by grace without rules and regulations. Keeping the law of Moses, far from making a person a better Christian, actually sought to make the cross of Christ ineffective (3:15-4:7, 5:2-12).
Since the Holy Spirit was given to the Galatians through faith as proof of their salvation, did they think that God expected them to work to be saved? (3:1-14). If they were brought to salvation by the power of the Holy Spirit, should they not continue to listen to His voice rather than mere men? (5:13-15). The false teachings of the legalists was incompatible and inconsistent with the sacrificial death of Jesus Christ for all men (2:11-21).
Paul expresses his deep sadness over those who had received the false teachings. Added to this was the fact that by accepting the legalists they were rejecting the person who taught them the word of God. (1:6-10). He warns those who remained faithful to stand firm against all such falsehood (6:1-10).