This thorn in the flesh is so painful, so overwhelming that Paul prays - three times - for God to remove it from him.
God doesn't. Why?
To humble him, yes. To keep him from boasting, yes.
But ultimately, so that Paul can boast - not in his strength - but in his weakness and in the sufficiency of God’s grace.
“My grace is sufficient for you, for my power is made perfect in weakness.” (2 Corinthians 12:9)