The central dispute in the letter concerns the question of how Gentiles could convert to Christianity, which shows that this letter was written at a very early stage in church history, when the vast majority of Christians were Jewish or Jewish proselytes, which historians refer to as the Jewish Christians. Another indicator that the letter is early is that there is no hint in the letter of a developed organization within the Christian community at large. This puts it during the lifetime of Paul himself.

This epistle addresses the question of whether Christians were obligated to follow Mosaic Law. After an introductory address (Gal 1:1–10), the apostle discusses the subjects which had occasioned the epistle.

In Chapter 1 he defends his apostolic authority (1:11–19; 2:1–14). Chapters 2, 3  and 4 show the influence of the Judaizers in destroying the very essence of the gospel. Chapter 3 exhorts the Galatian believers to stand fast in the faith as it is in Jesus, and to abound in the fruit of the Spirit. Chapter 4 then concludes with a summary of the topics discussed and with the benediction, followed by 5; 6:1–10 teaching about the right use of their Christian freedom. For example, it is clear that some took "freedom in Christ" as justification of antinomianism.

The issue of the Old Covenant in Christianity is complex and controversial, however, most traditional Christians believe much of it has been superseded while some modern Protestants believe it has been completely abrogated and replaced with the Law of Christ. Thus, "one who has Judaized", refers to a Christian who has accepted the necessity of adhering to the Mosaic Laws or to specific laws that are believed to be superseded, such as circumcision, Sabbath observance, or observation of the Passover. The ongoing Christian debate over "Judaizing in Christianity" began in the lifetime of the apostles, notably at the Council of Jerusalem and Incident at Antioch, and parallels the ongoing debate about Paul of Tarsus and Judaism, Protestant views of the Ten Commandments, and Christian ethics.

There is also a parallel to the debate within 1st and 2nd century Judaism as to the place of Gentiles with regard to the Torah. The outcome of that debate was that Rabbinic Judaism determined that gentiles need only follow a small subset of the Torah, called the Seven Laws of Noah, to be assured of a place in the world to come.