At first glance this is troubling; however, once you've identified it, you realize how very much God cares for you, that He would place something within our flesh to humble us, to keep us real. Paul described it as coming from Satan, a messenger sent to beat him when necessary. The necessary times are when Paul has received revelation. It's critical to understand that God has dominion over all, including Satan (read Job). Paul knows where to give credit for this affliction, yet remains steadfast in his trust of the Lord. Later passages explain how the weakest moments bring about God's strength and glory. Paul didn't revel in his own bravado during these times, but rather turned to the One who's grace is sufficient.
Have you identified the thorn in your flesh, the area in your life where you have the greatest weakness? Think, pray, and ask God to reveal it to you, although you probably already know what it is. It's the one area in your life where you are tempted the most by the enemy. In many ways, it feels like a thorn twisting into your side, causing immense pain, getting your undivided attention. Do you know what I mean?
This passage in 2 Corinthians speaks of our need to be aware of our weaknesses, but to not try to strengthen them or get rid of them. Rather, we are to see them as tools the Lord uses to mold us and shape us into His likeness. His glory is what matters, not our discomfort.
His grace is sufficient.