Obviously, Paul is a Christian. In those verses, Paul was speaking concerning of the Jews, to be a Jew inwardly, circumcision is that of the heart, in the spirit of the law, not the letter of the law. Paul was addressing a problem the Jews had.
Paul was expressing how the religious Jews were missing the mark in their strict, over emphasis to keep the law that over time had been complied into what the Jews call the oral law.
For example, the religious Jews criticized Jesus for Him healing a person on the Sabbath, i.e for not keeping the letter of the law. Jesus rebuked the hypocrisy of their criticism them by saying that they themselves would rescue one their cattle if it became in need on the Sabbath.
Jesus is the Lord of the Sabbath. Mark 2:27-28.