6 “I am astonished that you are so quickly deserting him who called you in the grace of Christ and are turning to a different gospel”
Paul bursts in with a rebuke, he doesn’t hesitate with addressing issues. He goes right in with the opening verse here that he is astonished that they have departed from the true Gospel so quickly.
In every Pauline epistle the introduction is always filled with thanks to God for the recipients and a lengthy salutation by the Apostle, except for this one. Paul is so bewildered by the Galatians’ willingness to embrace false gospels. The matter of Sola Fide is so crucial to the Gospel that Paul has no time for a salutation, he is too offended by the Galatians’ having turned to works salvation. This is so important that there simply isn’t room to say “hello.” This is how fiery we are to be when a central tenet of the Gospel is denied or attacked. We are not called to play games of unity with people who deny the truth and want to hold hands with us in the name of unity.
This isn’t Paul calling them to the grace of Christ, but God himself; God’s grace comes to us at His initiative, by His call and not because we deserve it. We cannot do anything to earn His grace. The Galatians have fallen into the trap that every single cult or false religion has fallen in to. They believe a false Gospel, they have left Christ, and moved towards works-salvation, or prosperity or something else entirely. The letter to the Galatians should be a warning to us just as it was to them to stick to the straight and narrow road. Continue to be in the Word; to increase in your knowledge and discernment.