Note 3 at 2 Cor. 13:3: Paul was the apostle over the Corinthian church. That gave him the highest level of authority in that body of believers (1 Cor. 12:28). But Paul's apostleship had been challenged (see Overview in Introduction to the Book of 2 Corinthians, p. 972). That's the reason he had written the letters we call First and Second Corinthians (see note 1 at 2 Cor. 1:1, p. 974; note 3 at 2 Cor. 1:12, p. 979; note 1 at 2 Cor. 2:1, p. 982; note 5 at 2 Cor. 3:3, p. 988; note 1 at 2 Cor. 11:1, p. 1033; and note 20 at 2 Cor. 11:13, p. 1036).

It is this challenge to his apostleship to which Paul is referring. Some had come to doubt that it was really God who spoke through Paul. He had been criticized over physical things (2 Cor. 10:10) and these weaknesses had been used to discredit his whole ministry. Paul is saying his ministry to the Corinthians had not been weak, but mighty through God, and they were the proof of that. They were born again (see note 2 at Jn. 3:3, p. 92) because of God working through Paul.