I told you before - That I would not spare offenders; that I would certainly punish them. He had intimated this before in the First Epistle 1Co 4:21; 1 Corinthians 5:1-13.
And foretell you - Now apprise you of my fixed determination to punish every offender as he deserves.
As if I were present, the second time - The mention of the second time here proves that Paul had been with them but once before. He had formed the resolution to go to them, but had been disappointed. The time when he had been with them is recorded in Acts 18:1 ff. He now uses the same language to them which he says he would use if he were with them, as he had expected to be, the second time. See the remarks of Paley on this passage, referred to above.
And being absent - see the note on 1 Corinthians 5:3.
To them which have heretofore sinned - To all the offenders in the church. They had supposed that he would not come to them 1 Corinthians 4:18, or that if he came he would not dare to inflict punishment, 2 Cor. 9-11. They had, therefore, given themselves greater liberty, and had pursued their own course, regardless of his authority and commands.
I will not spare - I will punish them. They shall not escape.