The Bible contains many stories of deliverance - Lazarus and Bartimaeus, to name only two. But our lives seem often to be deliverance-free. Paul, in the text, had a thorny situation like this - Christ did not grant his prayer's request. Let's look deeper - no shortcuts here! - to see how today's lesson applies to our lives. To do this, study the entire context.
2 Corinthians 12 (chapter context): the end of Paul's fourth (two were lost) letter to the Corinthian church. Book context: false preachers, looking for personal gain, were preaching that Christianity necessarily leads to monetary and worldly success. Paul rebutted this notion with the exact opposite, that his (Christ's) message is true. To cap it off, he boasted in his sufferings, his weakness. This segues into his thorn account.
The thorn was given him because he had seen infinitely wondrous things in visions. But what did he boast in? His thorn! A humble preacher of the Cross is weak to keep him, as with Paul, reliant on God's grace. Keep in mind that God is not the author of evil. Does He stop all evil and disease, then? No. It's a fallen world, which He allows to run its course.
Three times Paul pleaded for a miracle. His motives (unlike most of ours) are good - surely the thorn's removal would improve his proclamation of the Gospel! But Christ chose that Paul would remain weak in the body in order to point continually to Jesus Christ and His cross. Therefore he takes the lesson to heart: "For when I am weak, then I am strong." So God answers prayer in many ways, but very often calls for us just to rely on Him. Deliverance may be long in coming or even absent, but through all suffering we are to praise and trust in God as your God.
Soli Deo gloria. Amen.