‘For out of much affliction and anguish of heart I wrote to you with many tears, not that you should be made sorry, but that you might know the love that I have more abundantly to you.'
For the truth was that he loved them dearly, so much so that the severe letter had cause him much anguish of heart. Composing it had not been easy. It had been a great burden to him. And his prime intention had not been to make them sorry, although that had been necessary, but in order to show that he really cared about them, and that what he was requiring as an Apostle was really for their benefit, and was because of his concern and love for them.
This statement would seem to confirm that the letter referred to is not 1 Corinthians, but an unknown letter, because while he had been firm in 1 Corinthians, there is nothing about it that suggests tears of anguish.