From Second Corinthians by Thomas Stegman, SJ, commenting on Second Corinthains 12:9:
We finally reach the pinnacle of Paul’s entire boast in the second half of verse 9. Having heard the risen Lord’s response to his prayer, Paul settles on a different course of action, indicated by the conjunction “consequently” (not translated by the NAB). As a consequence of the Lord’s word to him about divine grace in human weakness, rather than praying for the thorn’s removal, Paul resolves to boast most gladly of his weaknesses. Paul has shed the use of irony here. He is perfectly serious about this boast because it serves an essential purpose: in order that the power of Christ may dwell with me. It is important to note that Paul is not saying that boasting of his weaknesses in and of itself activates the “power of Christ”; grace is a divine gift, not subject to human manipulation.
Instead, Paul’s wording here suggests two things. First, he chooses to draw attention to his weaknesses rather than to things like his religious heritage and apostolic accomplishments, because he wants others to recognize that it is Jesus who is working through him. Boasting about his weaknesses is, paradoxically, a way of boasting about the Lord (see 10:17). Second, Paul intimates that boasting of one’s weaknesses is valuable for one’s spiritual life. The more we are aware of our personal inadequacies, the more inclined we are to turn in prayer to the risen Lord and open ourselves to the grace he generously offers.