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.
Related Commentaries of 2 Corinthians 12:3
2 Corinthians 12:3
3 And I knew such a man, (whether in the body, or out of the body, I cannot tell: God knoweth;)