And it came to pass, that, when I was come again to Jerusalem, even while I prayed in the temple, I was in a trance; When I was come again to Jerusalem - It is likely that he refers to the first journey to Jerusalem, about three years after his conversion, Acts 9:25, Acts 9:26, and Galatians 1:18.
I was in a trance - This circumstance is not mentioned any where else, unless it be that to which himself refers in 2 Corinthians 12:2-4, when he conceived himself transported to the third heaven; and, if the case be the same, the appearance of Jesus Christ to him, and the command given, are circumstances related only in this place.