Paul expresses astonishment that the believers in Galatia were so quickly turned away from the grace of Christ to "another gospel." They had been called by the gospel of the grace of God and had received a secure standing in Christ through faith alone. Yet false teachers had persuaded them to exchange the liberty found only by God's grace for the bondage of the law.
The gospel of the grace of God is the power of God unto salvation and the foundation for our Christian walk. The believer's identity and standing in Christ sets him or her free to serve God out of gratitude rather than obligation. For this reason, we must defend the truth of God's grace and reject teachings that place believers back under the law. It is only in liberty, set free from the law, that we can serve God.