What was Paul’s thorn in the flesh?

In 2 Corinthians 12:7 because of the abundance of revelations he was given (one in particular fourteen years prior) God gave him a thorn in the flesh, a messenger of Satan to continually buffet him so pride would not take place. To buffet means to strike with the fist, it is related to physical violence (what was done to slaves). The thorn in classical Greek was in the sense of a pale or stake (Vincent’s Word Studies).

Paul had this continued affliction. The source in this case was Satan's messenger, which many suggest may have been a personal physical affliction not just the constant opposition of those hostile to him.

Scripture alludes to Paul having a physical affliction. We should note Satan is often attributed to be the afflicter of the body in the New Testament. In the gospels demonic activity is often accompanied with pain and some form of disease (Luke 13:16; Acts 10:38). In Vv.9-10 Paul laments, “Concerning this thing I pleaded with the Lord three times that it might depart from me. And He said to me, “My grace is sufficient for you, for My strength is made perfect in weakness.” God did not heal Paul’s thorn in the flesh (2 Corinthians 12:9-10). It was in his FLESH, it was a PHYSICAL infirmity and Jesus said NO to his request for healing three times. The Lord’s answer to Paul was NO. So to the many that believe God does heal everybody all the time; Paul was not a recipient of healing. The Lord did not cause it to be there, but allowed it. Instead, God’s will had determined Paul’s afflictions. God appointed it and God’s grace was there for his malady. Paul surrendered to the will of God in his situation. God said NO to Paul’s request for healing because God had a greater purpose in saying no. Paul understood the benefits; it brought dependence. This is the very opposite of “faith teaching” which says because a person is whole and strong physically, God’s power must be in there. He had a messenger from Satan to live with. He didn’t keep striving to be free from it, as no amount of faith would have removed it. It was God’s will and Paul accepted it. God’s answer was His grace. God’s power was then exhibited in Paul’s life because of his affliction.

Paul goes on to say, “Therefore most gladly I will rather boast in my infirmities”…“Therefore I take pleasure in infirmities, in reproaches, in needs, in persecutions, in distresses, for Christ’s sake.” This was so “that the power of Christ may rest upon me”… “For when I am weak, then I am strong” (2 Corinthians 12:9-10). Paul’s obstacles in his life became his pulpit. He was able to preach Christ with more conviction. His weakness was a physical handicap, and the result of this suffering kept him continually broken and dependent on the Lord’s strength. Infirmities, Astheneia in Greek; means a feebleness that has to do with strength, a weakness in the mind or body. This can be caused from disease, sickness, (used in various places like Matthew 8:17; Luke 5:15, 13:11; John 5:5; 1 Timothy 5:23). Paul’s weakness became his asset. This human flaw he possibly carried throughout his whole ministry became an opportunity for God’s strength to be manifested, and God was glorified.
To the Galatians he said “You know that because of physical infirmity I preached the gospel to you at the first. And my trial which was in my flesh,” Paul goes on to say “For I bear you witness, that if possible you would have plucked out your own eyes and given them to me” (Galatians 4:13-15, 6:11). This most likely alludes to the kind of affliction Paul struggled with -his eyes. So God can use even those who are weak and sick, sometimes those who are in this condition are more surrendered than those who are physically healthy and strong. 

God “comforts us in all our tribulation, that we may be able to comfort those who are in any trouble, with the comfort with which we ourselves are comforted by God. For as the sufferings of Christ abound in us, so our consolation also abounds through Christ” (2 Corinthians 1:4-5). Suffering has value in that those who have gone through it can minister comfort to others who also suffer. Our sufferings and hurts build compassion in us for others, and we are able to minister healing to them.