Verse 17
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, Act 9:25, Act 9:26, and Gal 1:18.
I was in a trance - This circumstance is not mentioned any where else, unless it be that to which himself refers in 2Cor 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.