A.T. Robertson Commentary 2 Corinthians 13:2

"I have said beforehand, and I do say beforehand, as when I was present the second time, so now, being absent, to them that have sinned heretofore, and to all the rest, that, if I come again, I will not spare;" — 2 Corinthians 13:2 (ASV)

As when I was present the second time (ως παρων το δευτερον). This translation assumes the second visit as already made. It is a natural way to take the Greek ως παρων. But ως with παρων can also mean "as if present" the second time (Authorized Version). Probably "as when" is the more natural rendering, but the other cannot be ruled entirely out in view of 1:15-23.

If I come again (εαν ελθω εις το παλιν). Condition of third class. The use of παλιν of itself suits the idea that Paul had not yet made the second visit as it means simply "again" or "back," but in Mt 26:44 we find παλιν εκ τριτου (again a third time) and so it is not decisive.