Galatians 4 shows that both legalism and idolatry are forms of spiritual slavery that reject the freedom found in Christ. Paul uses the image of a child-heir under a guardian to illustrate that, before faith, people are enslaved to “elementary principles”—whether the Jewish law or pagan gods. But when Christ came, he redeemed us, adopted us, and sent his Spirit into our hearts so that we cry “Abba, Father.” Christians are not slaves but sons, and we are called to live out that sonship through knowing the truth, praying as children to our Father, and serving others in love—rejecting anything that would pull us back into trying to earn what has already been freely given.

Instead of opening this letter to the Galatian churches with a thanksgiving for them — as Paul normally does — he begins by stating that he is astonished that they are so quickly deserting Jesus. The Galatians didn’t think that they had deserted Jesus! But Paul labors for Christ formed in them through the book of Galatians by demonstrating that departing from true gospel doctrine is deserting Jesus himself. In these first handful of verses, Paul sets out the terms of true gospel doctrine.