It is only about 3 years since Paul first travelled to the province of Galatia with the gospel message about Jesus. But already, a strong pressure group from Jerusalem was trying to add extra requirements to the gentile converts. They must believe in Jesus, but they must also be circumcised, and they must also keep the law of Moses. They were preaching a gospel of Jesus plus other things, and they had gained a strong foothold in the province of Galatia.
In this letter, Paul seeks to undo that influence and restore the churches to the solid foundation of the gospel he originally preached to them—the gospel we also have received and the gospel that is still preached all over the world. He summarises this message in the opening section of his letter.