rationalskepticism.org

In The Epistle to the Galatians -

The relation in which Paul as writer stood to his readers is a mystery. ....

The tradition, then, that Paul wrote this Epistle to the Galatian churches is anything but probable. ...

In the Conclusion:

Everything, therefore, points to the origin of Paulinism in Gnostic sources. It does not emanate from Palestine. If Rabbinical dialectic is to be found in the letters, this is to be explained by the nature of the polemic; the writer who is arguing against Jews, brought up in the traditions of Pharisaic Legality, is most likely to be successful by using their own methods of argument. But the Four Letters also contain a number of passages which show points of contact, both in form and matter, with the Cynic Diatribe - i.e., with the missionary preaching of ethical teachers of the Cynic and Stoic schools.

The writers of the Pauline letters speak Greek and think in Greek. When Paul in Rom 1:14 (cf. 1 Cor 14:11), calls himself a debtor, both to "Greeks and barbarians," such an expression proceeds from the national consciousness not of a Jew, but a Greek. That the man should pray with uncovered head and the woman with her head covered was a Greek and Roman custom; it is Paul's teaching in 1 Cor 11:4-7. Whenever he speaks of Jews and Judaism, he always leaves the impression that he himself occupies an outside standpoint. Take for example the following passages:

"If thou (proudly) namest thyself a Jew, and reliest on thy possession of the Law, and dost glory in standing in a special relation to God..." (Rom 2:17);

"Is God a God of the Jews alone, and not also of the Gentiles?" (Rom 3:29);

"I became a Jew unto the Jews, in order to win the Jews" (1 Cor 9:20)

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No one who [88] read these words without knowing who is supposed to have written them could possibly regard the writer as a born Jew.

http://www.depts.drew.edu/jhc/eysingsp.html