If the stereotype of striving for works-righteousness usually drawn from Paul does not fit first-century Judaism, the obvious alternative is to test the reverse correlation: Does the Jewish doctrine of salvation as outlined by Sanders provide a closer 'fit' with the views Paul rejected? I believe the answer is Yes, and have tried to make a beginning to arguing the case in the 1982 Manson Memorial Lecture. My conclusion there is that what Paul was objecting to was not the law per se, but the law seen as a proof and badge of Israel's election; that in denouncing 'works of the law' Paul was not disparaging 'good works' as such, but observances of the law valued as attesting membership of the people of God-particularly circumcision, food laws and sabbath. The theological rationale opposed by Paul was straightforward and firmly rooted in the Scriptures: Israel was the elect nation; the covenant promises were given to the descendants of Jacob; forgiveness and atonement were provided for the people of God through the law of Moses. Therefore to be a beneficiary of God's righteousness, the saving acts covenanted to his people, it was necessary to be a member of that covenant people. That meant, in the first place, circumcision-the terms of the covenant with Abraham left no room for dispute about that (Gen. 17.9-14). But membership of the elect people also meant life-long observance of the law, particularly those regulations which characterized and marked out the Jews in their distinctiveness as the people of the one God-among which food laws and sabbath held places of particular prominence both in Jewish self-consciousness and in Greco-Roman perception of the Jews as a people.
It was this understanding of the law from which Paul broke away when he objected to works of the law. That is to say, he objected to works of the law as limiting the the grace of God, not because they constituted impossible merit-earning demands, but because they were so firmly identified as distinctive marks of the Jewish nation and so in effect confined the grace of God to members of that nation. This is basically the position Paul maintained at and in the light of the Antioch incident (Gal. 2.11- 18) and the case he subsequently elaborated in Romans 3-4 and 9-10.
from pages 11-12, Jesus, Paul and the Law