Albert Barnes Commentary 2 Corinthians 12:21

"lest again when I come my God should humble me before you, and I should mourn for many of them that have sinned heretofore, and repented not of the uncleanness and fornication and lasciviousness which they committed." — 2 Corinthians 12:21 (ASV)

And lest, when I come again, my God will humble me, etc. Lest I should be compelled to inflict punishment on those whom I supposed to have been converted under my ministry. I had rejoiced in them as true converts. I had counted them as among the fruit of my ministry. Now, to be compelled to inflict punishment on them as having no religion would mortify me and humble me. The infliction of punishment on members of the church is a kind of punishment to him who inflicts it, as well as to him who is punished. Members of the church should walk uprightly, lest they overwhelm the ministry in shame.

And that I shall bewail many, etc. If they repented of their sin, he could still rejoice in them. If they continued in their sin until he came, it would be to him a source of deep lamentation. It is evident from the word "many" here that the disorders had prevailed very extensively in the church at Corinth. The word rendered "have sinned already" means "who have sinned before;" and the idea is that they were old offenders and had not yet repented.

The uncleanness. See Romans 1:24.

And fornication, and lasciviousness, etc. See 1 Corinthians 5:1; 1 Corinthians 6:18.

This was the sin to which they were particularly exposed in Corinth, as it was the sin for which that corrupt city was distinguished. See the Introduction to the First Epistle. Hence the frequent cautions in these epistles against it; and hence it is no wonder that some of those who had become professing Christians had fallen into it. It may be added, that it is still the sin to which converts from the corruptions and licentiousness of paganism are particularly exposed.