John Calvin Commentary 2 Corinthians 7:9

"I now rejoice, not that ye were made sorry, but that ye were made sorry unto repentance; for ye were made sorry after a godly sort, that ye might suffer loss by us in nothing." — 2 Corinthians 7:9 (ASV)

Not because you have been made sorry. He means he feels no pleasure whatever in their sorrow. Furthermore, if he had his choice, he would strive to promote equally their welfare and their joy by the same means. But since he could not do otherwise, their welfare was of so much importance to him that he rejoiced they had been made sorry to repentance.

For there are examples of physicians who are, indeed, in other respects good and faithful, but are at the same time harsh and do not spare their patients. Paul declares that he is not of such a disposition as to use harsh cures when not compelled by necessity.

However, since it had turned out well that he had tried that kind of cure, he congratulates himself on his success. He uses a similar form of expression in 2 Corinthians 5:4:

We in this tabernacle groan, being burdened, because we are desirous not to be unclothed, but clothed upon.