Why did Paul have to defend his apostleship?
Paul continually defended his apostleship because his background was steeped in Judaism: he was a Pharisee of the Pharisees, of the tribe of Benjamin, possibly a member of the Sanhedrin, and a Jew's Jew. He also described himself as the least of the apostles, which contributed to the need for defense.
Les teaches that Paul, described as the least of the apostles, had to always defend his apostleship, and no wonder. Paul had been steeped in Judaism. He was a Pharisee of the Pharisees, of the tribe of Benjamin. Les thinks he may have been a member of the Sanhedrin. He was a Jew's Jew. This deep Jewish heritage made his apostolic authority something he continually had to defend.