Commentaries:
Paul turned what could have sent him into deep bitterness and passivity (an affliction God decided not to heal when Paul felt he needed it) into a strength (humility and a deeper reliance on God). As painful, frustrating or hindering as it was, his circumstance never deterred him from being an apostle who by the grace of God labored more abundantly than all others (I Corinthians 15:10).
John W. Ritenbaugh
The Sovereignty of God: Part Two
These verses show us two examples regarding prayer: First, it illustrates how God can respond to our prayers, and second, how Paul reacted to God's answer. We, like Paul, want God to remove our afflictions any time we are in discomfort, but especially when the affliction is chronic and, we feel, inhibits accomplishment. God's response to Paul, however, fit a far greater need, perhaps to keep Paul humble so that his many gifts did not become a curse. Instead, God gave him strength to bear up under the affliction, thus keeping him in a constant state of dependency for strength to go on. Paul humbly accepted this and continued his ministry despite his affliction, knowing it was fulfilling God's will.
John W. Ritenbaugh
The Sovereignty of God: Part Nine
Other commentary entries containing this verse:
Colossians 3:12
Titus 3:1-2
1 Peter 5:5