How could anyone desert the gospel quickly? Two answers seem apparently obvious. Either, they didn't grasp the significance of it, especially in regard to the Law; or, they didn't have full confidence in the credentials of Paul, who delivered it to them.
This letter addresses the significance of the Gospel--as emerging from the Promise--in contrast to the Law--as being added to control a sinful people until the Promise could be fulfilled. But, more to the point in our first discussion, chapters one & two introduce the problem of desertion and address Paul's credentials as Christ's spokesman.
Judaizers were the problem. They and their message--circumcision and Law-keeping were essential to salvation (cf. Acts 15:5)--were "disturbing" the Galatians. That is, rather than enjoying the peace of the Gospel they were agitating over the physical demands of the Judaizers and the emotional upset of doubting their stand with God.
Paul was truly and fully an apostle of Jesus Christ. His conversion proves it (Gal. 1), his message proves it (Gal. 1), his bold stand agains circumcision for Titus proves it (Gal. 2; Acts 15) and his rebuke of "the great" apostle Peter proves it (Gal. 2). Tune in or download and join the discussion as we check out Paul's right to speak.