After an introduction (1:1–5), Paul rebuked the Galatians for turning to false gospel and cursed those who preached it (1:6–10). This false gospel was that one had to add the Law of Moses to his faith in order to be righteous, shown representatively by being circumcised. As Paul would explain, if this “gospel” were true, hearing the gospel with faith was unnecessary, and one could earn his own righteousness by keeping the Law.
In showing this “gospel” to be false, Paul gave the story behind the true gospel that he preached and how it was confirmed by others. He received it from Jesus Christ (1:11–17) and was confirmed of its truth two times by Peter in Jerusalem, the second time along with Peter and John (Gal 1:18–2:10). He even confronted Peter for acting out of accord with what he had previously confirmed (2:11–14). Summarizing his gospel in contrast to the heresy at hand, Paul stated that “a person is not justified by works of the law but through faith in Jesus Christ” (2:16; cf. 2:15–21).
Explaining the role of faith further, Paul reminded that it was through faith that the Galatians received the Spirit, persevered, and saw miracles (3:1–5). And, just as Abraham was saved by faith without the Law, so also their salvation came in the same way (3:6–9). Relying on the Law was impossible and brought about a curse that is canceled only through the work of Christ on the cross (3:10–14). The purpose of the Law was to show how sinful man was and that his ability to keep it was impossible. When Christ came, this temporary function of the Law ended, and now we live by faith in the gospel through the Spirit (3:15–4:11).
After exhorting his readers to continue in the gospel they had once so gratefully received (4:12–20), Paul intentionally allegorized the story of Hagar and Ishmael and their relation to Sarah and Isaac to illustrate how the Galatians were now enslaving themselves to the Law, persecuting those who had the Spirit, and were not acting as heirs of the New Jerusalem (4:21–31).
Paul again exhorted them to stand firm in the gospel and not accept circumcision as the basis for their righteousness, something of no advantage that would sever themselves from Christ (5:1–6). He was confident that they would return to the gospel (5:7–12) and detailed a life lived by the Spirit in contrast to a life lived in the flesh (5:13–26).
Giving general instructions that likely dealt with a matter at hand, Paul commanded that any transgressor (such as a false teacher) should be restored and treated gently, not thinking themselves better than the transgressor but boasting, if anything, in Christ (6:1–5). Influenced by false teachers, the Galatians may have waned in their giving to the church, so Paul commanded them to share their good things (e.g., finances) with their teachers, promising spiritual reward (6:6–10).
Paul closed the letter by once more attacking the false doctrine of finding righteousness by keeping the Law, promising peace and mercy to those who could boast instead in the cross of Christ (6:11–18).