Apparently, the members of the congregations of the new churches Paul was setting up were hearing conflicting messages. They were hearing one thing from Paul, and something completely different from "the Judahizers", the followers of the teachings of the Jerusalem church, of which the top guy was James, the brother of Jesus. Paul was arguing his case that he knew more about what it took to be saved than James did.
Thanks.
It would seem it treats with the argument that faith trumps good works.