2 Corinthians 7:9

Having said, "I do not regret," he tells the reason also; alleging the good that resulted from his letter; and skillfully excusing himself by saying, "though but for a season." For truly that which was painful was brief, but that which was profitable was perpetual. And what indeed followed naturally was to say, 'even though it grieved you for a season, yet it made you glad and benefited you forever.' But he doth not say this: but before mentioning the gain he passes again to his praises of them, and the proof of his own concern for them, saying, "Now I rejoice, not that ye were made sorry," ('for what gain came to me from you being made sorry?) "but that ye were made sorry unto repentance," that the sorrow brought some gain.' For a father also when he sees his son under the knife rejoiceth not that he is being pained, but that he is being cured; so also doth this man. But observe how he transfers all that was well achieved in the matter unto themselves; and lays whatever was painful to the account of the Epistle, saying, "It made you sorry for a season;" whilst the benefit that resulted from it he speaks of as their own good achieving. For he said not, 'The Epistle corrected you,' although this was the case; but, "ye sorrowed unto repentance." "For ye were made sorry after a godly sort, that ye might suffer loss by us in nothing." Seest thou wisdom unspeakable? 'For had we not done this,' he says, 'we had done you damage.' And he affirms that indeed which was well achieved to be theirs, but the damage his own, if indeed he had been silent. For if they are likely to be corrected by a sharp rebuke, then, if we did not sharply rebuke, we should have done you damage; and the injury would not be with you alone, but also with us. […]

Seest thou wisdom unspeakable? 'For had we not done this,' he says, 'we had done you damage.' And he affirms that indeed which was well achieved to be theirs, but the damage his own, if indeed he had been silent. For if they are likely to be corrected by a sharp rebuke, then, if we did not sharply rebuke, we should have done you damage; and the injury would not be with you alone, but also with us. For just as he that gives not to the merchant what is necessary for his voyage, he it is that causeth the damage; so also we, if we did not offer you that occasion of repentance, should have wrought you damage. Seest thou that the not rebuking those that sin is a damage both to the master and to the disciple?

Then he gives the reason for his joy, because I am not glad that you were made sorrowful, but at the effect, namely, your amendment, because you were grieved not unto despair, but you were grieved into repenting; just as a physician is not glad …

The sorrow was temporary – for an hour, but the benefit was everlasting. "I rejoice," he says, "not because you were grieved" (for what benefit is your sorrow to me?), "but that you were grieved to repentance." Notice how he attributes the sorrow to repentance, …

Now I rejoice, not that ye were made sorry,....