To keep me from becoming conceited because of these surpassingly great revelations, there was given me a thorn in my flesh, a messenger of Satan, to torment me. Three times I pleaded with the Lord to take it away from me. But he said to me, "My grace is sufficient for you, for my power is made perfect in weakness." Therefore I will boast all the more gladly about my weaknesses, so that Christ's power may rest on me. (NIV)
After Paul had explained his visions and revelations to the Corinthians (2 Cor 12:1-6), he tells them about the thorn in the flesh that was given to him. The apparent purpose of this thorn was beneficiary. Its intent was to keep Paul from conceit on account of his visions and revelations which otherwise may have given him a reason to boast.
There have been many theories as to what exactly this thorn wasso many theories in fact, that it is impossible to diagnose Paul's situation with complete assurance. Some have suggested that Paul's thorn came in the form of Jewish persecution because of the surrounding context speaking of opponents. Even in Numbers 33:55 thorns are used as a metaphor for the enemies of the Israelites. Others have suggested that Paul's own remembrance of his past was his thorn; Paul's past included the persecution of the church (Acts 8:1-3; Gal 1:13; Phil 3:6) which may have continually haunted him and kept him humble. Some even propose that Paul dealt with either carnal temptation or depression.
A physical ailment, however, seems more likely here, though the lack of details forbid a proper diagnosis. Physical infirmities that seem to fit the situation are malaria, Malta fever, epilepsy, convulsive attacks, and chronic ophthalmia.
Many of these physical disabilities also affect the eyesight and it seems probable that even Paul himself experienced difficulty with his visionthis could very well be caused by his thorn in the flesh. Paul took advantage of various amanuenses to do the actual writing of at least some of his epistles. A mentioned amanuensis of Paul is Tertius who wrote down the book of Romans and added his own greeting to the church in Rome (Rom 16:22). Other times we see Paul adding a salutation with his own hands (1 Cor 16:21; 2 Thess 3:17) as opposed to physically writing the entire epistles. Paul even wrote in large print as noted in Gal 6:11. Other evidences of poor vision can be found earlier in the epistle to the Galatians. Paul says that because of physical infirmity he preached the gospel to the Galatians at the first (Gal 4:13). Some have speculated that the physical infirmity was a disease which affected his eyesight and the higher altitude in Galatia would have been better for him, especially if the disease was malaria. And only two verses later Paul states that the Galatian church would have plucked out their own eyes and given them to him if it were possible (Gal 4:15). Another example of Paul's poor eyesight is found in Acts 23:3-5. Paul was in the Sanhedrin at this point and referred to the high priest as a "white-washed wall" and those who stood by him asked why he was insulting the high priest. Paul responded by telling them that he did not realize that the man was the high priest. Though Paul, previously being a Pharisee, would have been able to recognize the high priest quite easily. Yet at this point he seemed unable to identify the high priest, even though the high priest would have stood out because he wore special garments and accessories. For a former Pharisee to have not recognized him is likely explained through understanding that Paul was not able to see him properlygiving weight to theories of trouble with his vision.
Paul's thorn came by way of a messenger of Satan in order to torment him. Yet at the same time it was given to him in order that he would not become conceited. The present paradox can be compared to that of the story of Job. Satan was permitted to afflict God's servant, yet only within the parameters set by God (Job 2). Paul also wrote about handing an immoral brother to Satan so that his flesh may be destroyed and his spirit saved on the day of the Lord (1 Cor 5:5). Satan is used at times as an instrument to bolster the faith or prove the righteousness of believers.
The ambiguity of the thorn in the flesh is actually a positive thing. If Paul would have specifically stated the identity of his thorn, believers from following generations may have discarded his experience if they were not afflicted with the same affliction. However, Christians from many generations have benefited by his reference to the thorn while applying it to their specific problems (Murray J. Harris. The Expositors Bible Commentary: 2 Corinthians. Grand Rapids: Zondervan Publishing House, 1976. p. 396). The thorn of which Paul speaks gives us an understanding of God's perspective concerning physical infirmities. Sometimes God uses illnesses for his purposes. Paul experienced many sufferings outside of his thorn (2 Cor 11:22-28), yet God used him mightily for the furtherance and advancement of His Gospel. The existence of illness or suffering in a believer's life does not necessarily constitute a sinful life or a life that lacks faith. Paul pleaded with the Lord on three separate occasions for the Lord to remove the thorn, yet God's grace was enough for the apostle and His power is made perfect in Paul's weaknesses.