Francis Watson frames the basic difference between Paul and Judaism as one of distinct views of divine and human agency. He is clear that it is not simply divine grace vs poor form of Pelagianism. His reading has a payoff value when interpreting the notoriously difficult Romans 2.7-13, regarding those that pursue the good receiving life and those that do the law are justified. He argues:

Belief in judgment by works is indeed an integral part of Paul’s theology…[citing Rom 8.13, Gal 6.8, 5.21; Rom 2.9-10, etc.]…[The “good” that humans do] is grounded in God’s prior saving action, which establishes and enables an appropriately directed human agency. This is not “salvation by works” as commonly understood, that is as a salvation attained by unaided human effort. But nor is is “salvation by grace” as commonly understood, that is as a salvation in which the one who is saved stands in a purely passive relationship to the one who saves. Divine and human human agency do not conexist on the same plane, in such a way that more of one means less of the other. Rather, God’s prior grace works in and through the human agent, whose reoriented and free agency is itself the work of grace. (Paul, Judaism, and the Gentiles, rev. ed., 214)

I noticed that John Barclay makes a similar claims non-contrastive agency in his Paul and the Gift about Romans 2:

Eternal life is, for Paul, both an incongruous gift (6:23) and the fitting completion of a life of good work (2:6–7). (466, cf. 464–74)