See my reply to campion.
What would Paul of all people not forgive? A sin not repented of would not be forgiven. He is forgiving or not forgiving in the presence of Christ.
2 Corinthians 2:10-11
“Whomever you forgive anything, so do I. For indeed what I have forgiven, if I have forgiven anything, has been for you in the presence of Christ, so that we might not be taken advantage of by Satan, for we are not unaware of his purposes.”