It seems that everybody ever to write anything about this chapter ever has been convinced (against what is actually written) that Paul is talking about himself being caught up to the third heaven. So Paul is actually saying, "On behalf of myself I will boast, but on my own behalf I will not boast"? Really? How is that even possible? Is it supposed to be zen?12 I must go on boasting. Though there is nothing to be gained by it, I will go on to visions and revelations of the Lord. 2 I know a man in Christ who fourteen years ago was caught up to the third heaven—whether in the body or out of the body I do not know, God knows. 3 And I know that this man was caught up into paradise—whether in the body or out of the body I do not know, God knows— 4 and he heard things that cannot be told, which man may not utter. 5 On behalf of this man I will boast, but on my own behalf I will not boast, except of my weaknesses. 6 Though if I should wish to boast, I would not be a fool, for I would be speaking the truth. But I refrain from it, so that no one may think more of me than he sees in me or hears from me. 7 So to keep me from becoming conceited because of the surpassing greatness of the revelations,[a] a thorn was given me in the flesh, a messenger of Satan to harass me, to keep me from becoming conceited. 8 Three times I pleaded with the Lord about this, that it should leave me. 9 But he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” Therefore I will boast all the more gladly of my weaknesses, so that the power of Christ may rest upon me. 10 For the sake of Christ, then, I am content with weaknesses, insults, hardships, persecutions, and calamities. For when I am weak, then I am strong.
Surely the man in Christ is Jesus! Paul will boast in Jesus, not in himself. Who else does Paul know who went up to heaven and then spoke to him? Immediately before the story Paul (or 'Paul') introduces it by saying "I will go on to visions and revelations of the Lord." Then he describes a vision he had of the Lord (Jesus) being caught up to the heavens.
It's referring back to the end of the Gospel of the Lord (the previous book in the Marcionite Bible. It can't be GLuke because that begins with an explanation of how it was written which has nothing about visions or the Lord. I'd say GLord was written before the 'genuine' Pauline epistles.