Why did Paul have to always defend his apostleship?
Paul had to always defend his apostleship because he had been steeped in Judaism, was a Pharisee of the Pharisees from the tribe of Benjamin, and likely a member of the Sanhedrin. He was a Jew's Jew, and that background explains why he called himself the least of the apostles.
Les teaches that Paul, according to his own description, was the least of the apostles and had to always defend his apostleship. No wonder, Les explains, because Paul had been steeped in Judaism. He was a Pharisee of the Pharisees, of the tribe of Benjamin, and Les thinks he may have been a member of the Sanhedrin. In short, he was a Jew's Jew. This deep Jewish heritage and former standing made his apostolic authority something he continually had to defend. Les also notes that Paul's writings are the most neglected in Scripture today, and he gives that neglect as the reason for the demise of the church's power and spiritual weakness, even while churches may appear rich and full of members.
Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God,