Interesting description from J. Christiaan Beker on Paul's antagonists in Galatia--perhaps formulated a bit over-confidently, but fascinating nonetheless:
"The argument of the opponents runs along the following lines: You Galatians were Gentiles when, though the gospel which Paul preached, you turned to Christ. This turning away from idols and the "elemental spirits of the universe" (Gal 4:3,9) is an important first step. It is like the step Gentiles take when they turn from idols to the God of Israel and attach themselves as semiproselytes or God-fearers to the synagogue. However, do not mistake the first step for the end of the road (Gal 3:3). Paul misled you when he told you that your new status as sons of God in Christ depends on faith alone. This is an opportunistic misconstruction of the gospel and short-circuits its full implications. You realize--of course--that our Christ was the Messiah promised to the people of Israel, the true sons of Abraham. Jesus Christ is indeed the messianic fulfillment of the promise to Abraham, and therefore the promise pertains to those who belong to the people of Israel. It does not mean that Gentiles are excluded from the promise: They can participate in the full blessings promised to Abraham if they join the people of the promise. When Paul opposes the Torah and Christ, he is not only wrong but also opportunistic, because he wants to make it religiously and sociologically easy for Gentiles to become Christians, in order to enhance his apostolic grandeur. It is simply false that Gentiles can remain participants in pagan society without the "yoke of the Torah." The Torah and Christ cohere, because it is only within the realm of the Torah that the promise is fulfilled in Christ. To be sure, the observance of the Torah does not mean the observance of all its statutes and ordinances. Although Jesus Christ, the Messiah, acknowledged their validity, they have been fulfilled by him in his death for us. Nevertheless, "Torah-keeping" means the obligation to become a member of the Jewish people and therefore circumcision marks your entrance into the l;ine of salvation-history that started with Abraham and finds its fulfillment in Christ. The Torah, then, has primarily salvation-historical significance; it assures your participation in Christ by placing you in the correct salvation-historical scheme. What counts is its cosmic-cultic meaning as law of the universe. Therefore circumcision and Jewish calendar-observances (Gal 4:10) complete your status as full Christians and guarantee God's divine blessing upon you as true sons of Abraham. Paul should have taught you the gospel in this way. His claim to apostolic independence is actually a combination of opportunism and disobedience. His opportunism is directed at painless mass conversions, which must enhance his ego, whereas his disobedience is apparent when he--contrary to directions from Jewish-Christians headquarters in Jerusalem--preaches an abbreviated gospel. . . . this latecomer to the apostolic circle acts illegitimately and disobediently when he preaches a gospel that rests on sola fide, ignores the law and the Jewish antecedents of the Messiah, destroys the community of Israel wih the church, and lacks a proper ethic."
--Paul the Apostle: The Triumph of God in Life and Thought, 43-44