‘Sufficient to such a one is this punishment (‘censure, reproof, reprimand') which was inflicted by the many, so that, in contrast to that, you should rather forgive him and comfort him, lest by any means such a one should be swallowed up with his overmuch sorrow. Wherefore I beseech you to confirm your love towards him.'
It appears that in response to his severe letter the church has repented and meted out quite severe punishment on the offender, possibly in the form of a severe public reprimand and even exclusion from some of the benefits of the church, for example from the love feasts or from taking part in the services. Now therefore he feels that it is time for them to forgive him and reinstate him. The punishment inflicted by the majority of the church has been quite sufficient. It has resulted in his repentance. Now they must show forgiveness and come alongside to help him and comfort him, in case his sorrow and remorse becomes so overwhelming that it devastates him. So, says Paul, I beg you (or ‘urge you') to ‘confirm' your love towards him. ‘Confirm' has legal significance and suggests a specific act of restoration by which the man is assured of their love.
Most old commentaries identify this man with the man in 1 Corinthians 5 who was to be committed to Satan (cast out of the church). The main reason why this is unlikely is the personal hurt that this one has caused to Paul. While the man in question in 1 Corinthians sinned deeply, even though it distressed Paul it was not particularly against him. There was no reason there why Paul's forgiveness should especially be sought, whereas the man in view here has acted in such a way as to require precisely that. Nor is it clear how even such a dreadful kind of adultery should cause Paul the distress described in 2 Corinthians 2:4. The only way in which it could be so is if the same man had obtained sway over the whole church, and had led the attack on Paul. And would such a man have repented at Paul's letter if previously he had been so obdurate?
It is far more likely that this man was one who had sought to usurp Paul's place in the hearts of the Corinthians, possibly entering among them as a newcomer with letters of commendation from someone of importance, and had done it in a particularly obnoxious manner, with false insinuation and accusations, and a show of strength, probably assisted by special cronies. He had done it in such a subtle way that he had influenced many of the church sufficiently to cause them to side with him against Paul when Paul paid his unexpected visit. But he must have been to some extent genuine for him to be so repentant. He appears to have been a dupe of Satan rather than an evil man.