Paul writes to the Galatians to make them understand that by God’s grace they are no longer under the law. When the Gospel was preached to them, there were some among them of Jewish origin known as circumcisers—though they called themselves Christians—who did not grasp the gift they had received. They still wanted to be under the burden of the law. Now God had imposed that burden on those who were slaves to sin and not on servants of justice. That is to say, God had given a just law to unjust men in order to show them their sin, not to take it away. For sin is taken away only by the gift of faith that works through love. The Galatians had already received this gift, but the circumcisers claimed that the Gospel would not save them unless they underwent circumcision and were willing to observe also the other traditional Jewish rites.
From an explanation of Paul’s letter to the Galatians by Saint Augustine, bishop