John Calvin on 2 Corinthians 12:19

19. Do you again think. As those that are conscious to themselves of something wrong are sometimes more anxious than others to clear themselves, it is probable, that this, also, was turned into a ground of calumny — that Paul had in the former Epistle applied himself to a defense of his ministry. Farther, it is a fault in the servants of Christ, to be too much concerned as to their own reputation. With the view, therefore, of repelling those calumnies, he declares in the first place, that he speaks in the presence of God, whom evil consciences always dread. In the second place, he maintains, that he has not so much a view to himself, as to them. He was prepared to go through good report and bad report, (2 Corinthians 6:8,) nay, even to be reduced to nothing; but it was of advantage to the Corinthians, that he should retain the reputation that he deserved, that his ministry might not be brought into contempt.