Why did Paul have to defend his apostleship to believers in the age of grace?
Paul's apostleship required defense because believers in the age of grace needed to recognize him as the authority through whom God was speaking to the whole human race. Divisions and rival claims—some following Peter, some dismissing Paul—made establishing his apostolic authority essential.
Les explains that Paul opened his letters by establishing the authority connected to his apostleship; verse 1 says, “Paul called to be an apostle,” almost identical to his other openings. The Corinthian believers faced divisions: some claimed to follow Paul, some Peter, and others said they did not care what Paul said and would do what Jesus said. Paul was up against the same resistance. For believers in this age of grace, he had to establish that he was the authority through whom God was speaking to the whole human race. He was always defending that apostleship, especially to Jewish people, because they considered him a renegade to Judaism.
Paul, called to be an apostle of Jesus Christ through the will of God, and Sosthenes our brother,