Albert Barnes Commentary 2 Corinthians 12:3

"And I know such a man (whether in the body, or apart from the body, I know not; God knoweth)," — 2 Corinthians 12:3 (ASV)

And I knew such a man. It is not uncommon to repeat a solemn affirmation in order that it may be made more emphatic. This is done here. Paul repeats the idea that he was intimately acquainted with such a man, and that he did not know whether he was in the body or out of the body. All that was known to God.