Check this link out.
How God Uses Suffering--Part 1
http://www.biblebb.com/files/MAC/47-83.htm
"In fact, he describes this in verse 7 of our text in these words, "There was given me a thorn in the flesh, a messenger of Satan to buffet me." And I told you last time that this assault by the false teachers on the Corinthian church which resulted in their betrayal of Paul is here described as a "thorn in the flesh." He further describes it as a messenger of Satan. The messenger is the word angelos in the Greek, it means angel, and an angel from Satan is a demon and so he's telling us here that this terrible, terrible betrayal by the Corinthians, this defection from the true gospel and the truth that he had taught them, this was all being orchestrated by a demon. Demon-inspired false teachers had come into that church and perpetrated this terrible, terrible mutiny. And the effect of it was to buffet me, he said, and that's the word torment. Paul was personally tormented by the problems in the Corinthian church. Because he loved God so much he didn't want to see God dishonored, because he loved the gospel so much he didn't want to see it misunderstood, because he loved the church so much he didn't want to see it torn up and divided, because he loved those people so much he didn't want to see them fall victim to lying false teachers."
"Verse 7 says, "There was given me a thorn in the flesh." This, by the way, was a gift...however an unsolicited one, it was a gift, then it was really from God. We know that because in verse 8 he asks the Lord to remove it. God had allowed this to happen, as we saw God allowed Satan to assault Job, God allowed Satan to assault Peter. For His own purposes God will allow the devil to do His work. And in the end it will effect the divine purpose."
Read the whole thing it's worth your time.
Isaiah 48:10 "See, I have refined you, though not as silver; I have tested you in the furnace of affliction." Isaiah 48:10