What reason did the Lord give Paul for his thorn in the flesh?
The Lord answered Paul that His grace was sufficient for him, because His strength is made perfect in weakness. The thorn served to keep Paul humbled and dependent, so God's power could be displayed through a weak vessel rather than Paul's own ability.
Les explains that Paul's thorn in the flesh may have been a common eye disease of that period—repulsive, painful, and limiting his eyesight. That would explain why Paul dictated his letters, seemingly except Galatians, and wrote in huge block letters for his own sake so he could read. In II Corinthians 12:8 Paul asked the Lord three times that the thorn, this buffeting by an angel of Satan, might depart. The Lord Jesus Himself answered, 'My grace is sufficient for thee, for my strength is made perfect in weakness.' Les says God thereby gave the reason for keeping Paul humbled and allowing trials and sufferings. Les ties this to I Corinthians: Christian service must be done as a weak vessel God uses, because the minute we think we can do it ourselves, we are done.
And he said unto me, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities, that the power of Christ may rest upon me.