What the Bible says about Pagans
(From Forerunner Commentary)
Paul is most likely still addressing Peter and the other Jews who were acting unfaithfully. This flows smoothly from what Paul said to Peter "before them all" (verse 14), and it is not until the beginning of chapter 3 that Paul directly addresses the Galatians again.
They were Jews by nature, or by birth, as opposed to the Gentiles, who were, by definition, of a different race. Paul does not mean that one race was inherently righteous and the other was inherently sinful. However, the Greek word used here for "sinners" is hamartoolos, which often signifies a pagan, one who had no knowledge of the true God. This is not a condemnation of Gentiles in general, but rather a statement that they had no connection with God by heritage as the Jews did. Romans 14:3 states the principle that whatever is not of faith is sin, so anyone not knowing God—and thus not having faith in Him—would be a "sinner." To show further that Paul is not playing favorites, Romans 3:9 shows that both groups of people (Jew and Gentile) were sinners in terms of coming short of the glory of God and breaking His law.
David C. Grabbe