Rather than hide his flaws or deny his weakness, Paul reveled in the power of Christ that was revealed through him when he was afflicted, perplexed, persecuted and struck down (ways of describing even his “thorn in the flesh”). Of course to the Corinthians it was sheer folly to boast about such things. Paul didn’t care. He saw the essence of the gospel in his wounds, the wisdom of God in such foolishness, the power of God in human weakness. Where would he get an idiotic idea like that? Only one place: “Jesus Christ, and him crucified” (1 Cor 2:2). In what sounds like a confirmation of the cross, Paul heard God say, “My grace is sufficient for you” (2 Cor 12:9). That’s why boasting in his weakness is the same as boasting in the cross. He freely admits there were times when he was “afflicted…perplexed…struck down” (2 Cor 4:8-9), even “depressed” (2 Cor 7:6 NASB). For Paul was convinced that weak believers reveal the strength of Christ’s cross better than anyone.
Rodney Reeves, Spirituality According to Paul: Imitating the Apostle of Christ, 50.