Galatians is Paul's letter to the assemblies of Galatia (1:2). Paul opens by defending his apostleship, which came not from men nor through a man but through Jesus Christ and God the Father. His greeting already summarizes the Good News: Christ gave Himself for sins to rescue believers from the present evil age, according to the Father's will.
Unusually, Paul offers no thanksgiving. He is astonished that the Galatians are deserting God for a different gospel. Teachers were insisting that Gentile believers must keep the Jewish law, especially circumcision, to be fully accepted. Paul says such a message is not another gospel but a distortion. He declares that anyone who preaches a different gospel, even an angel, stands under God's judgment. He is not seeking human approval, for if he were, he would not be a servant of Christ.
Paul then gives his testimony to show that his gospel came by revelation, not human tradition. As a zealous Pharisee he violently opposed the church. But God, who set him apart from birth, called him by grace and revealed His Son in him so he might preach among the Gentiles. Paul did not immediately consult anyone. He went to Arabia and Damascus, and only after three years spent fifteen days with Peter, seeing also James, the Lord's brother. The Judean churches knew him only by report, and they glorified God because of him.