Does Paul have to deal with Jews who are confident that they are performing the law rightly, and believe that they have something to boast about before God because of their performance? Yes, of course. He’s dealing with Pharisees, of the kind that Jesus satirized in his parable, who boasted before God about his performance of the jots and tittles of the law and who believed that this gave him a standing before God above that of the publican. Unless Jesus was making it up, or unless this kind of Pharisaism disappeared by the time of Paul, Paul must be dealing with this as well.
Is this a key issue in Paul’s letters? Yes, in Romans at least. But it is not a key issue for exactly the reason that it has sometimes been thought. Surely Jesus and Paul address this to convict individual Jews of their sin and to urge them to repentance. But there is a bigger issue at stake. It’s crucial to Jesus because it’s this kind of hypocrisy that is leading Israel to ruin; Matthew 24 follows Matthew 23. It is a key issue in Paul because Israel’s impenitent sinfulness puts the salvation of the world at risk, and raises questions about God’s own righteousness and faithfulness (see earlier post).