Of course atonement was part of the law and one could ‘keep’ the law. I have no quibble with that at all. The interesting thing to note that is coming from the reaction to the NP is that as Moises Silva writes:
“The fact is that the apostle nowhere (in Galatians or in his other letters) characterizes his opponents as people who are obedient to the law. He will admit to no such thing. In this very epistle, as many have pointed out, he specifically accuses them of not keeping the law (6.13). And in Phil 3:2-4, when describing a group of opponents who, to say the least, had some affinities with the Judaizers in Galatia, he deliberately depicts them as pagans.” (*Abraham, Faith, and Works: Paul’s Use of Scripture in Galatians 3:6-14; Westminster Theological Journal 63 [2001] 251-67)
Gathercole addresses this in the context of Romans:
“It is an assumption of the New Perspective on Paul that the Judaism with which Paul was in dialogue shared a similarly patterened structure to his own, with a belief in election as the way in, and with works, combined with repentance and atonement to “stay in.” However, many traditional portraits
of Paul have treated Judaism as if there was no sacrifice system. In response, protagonists of the New Perspective maintain that Paul could not be accusing his dialogue partner of “self-righteousness” because any pious first-century Jew knew that he was a sinner (Prayer of Manasseh; 1QS 11) but that God had provided a means of dealing with sin, namely, the temple cult with its sacrifices. This approach is misleading for several reasons, which are relevant here in discussion of Romans 2. The minor objections are: first, there is evidence for a possible downgrading of the sacrificial system among various
groups within Second Temple Judaism well before the destruction of the temple. Second, one could raise the question of the validity of taking liturgical texts such as the Prayer of Manasseh or 1QS11 and deducing anything about the spiritual condition of people on the ground. The liturgy of any religious group could scarcely be described as an index of the spiritual vitality or its users.
Yet these are peripheral issues. The most important consideration that is consistently neglected is that Paul is essentially dealing with a dialogue partner (a representative, as we have seen, of the nation) *who is unrepentant*, and (though not visibly) an apostate. Thus, Paul would assume that the sacrificial system was not effective for him, and the interlocutor himself would have a wrong attitude toward it.” (pp. 205-206)
Gathercole goes on to quote Rom 2.5; 2.27-29; 9.31 and 10.2 in support of this thesis. I would add that David makes clear in Psalm 51 that sacrifices must be offered with a broken spirit and a contrite heart, that God “delights in right sacrifices” and that it was obviously very possible for even the sacrificial system to be of no effect for the prideful.