At the beginning of 2 Corinthians 10 Paul writes that he wants to be non confrontational toward them, but will be stern if necessary, warning them about living by the standards of the world.

“…we take captive every thought to make it obedient to Christ.”
When faced with temptation, it’s nice to have a Bible verse to quote in order to take every thought captive. Because we will be judged for every careless word we've ever spoken.

Many people said that Paul's letters were weighty and forceful but in person he was unimpressive. It seems that Paul was forceful in his letters. People read them, had time to digest them so that by the time Paul visited these people, there was no need for him to be forceful or confrontational.

2 Corinthians 10:7
You are looking only on the surface of things....

When reading the Bible if we only take the surface meaning, we miss learning about the "deep things of God."

1 Corinthians 2:10
But God has revealed them to us by His Spirit; for the Spirit searches all things, yea, the deep things of God. 

See the book Diving into Deep Things of God by Phil and Patti Moore available on Amazon.

Paul had some strong words to say, “When they measure themselves by themselves and compare themselves to themselves, they are not wise.”
Would this be ego-mania to the max!?!

“…for Satan himself masquerades as an angel of light”
Satan will use any means possible, including passing himself off as God, using both subtle and blatant means. He is the great deceiver. Satan is not omnipotent. He can’t make us do anything. We must be willing. Don’t give him too much credit.

Notice all the sufferings Paul lists. With all the punishment his body received, he probably never fully recovered from any of them. Can you imagine suffering without pain medication or the comfort of our homes and people to take care of us? Being a believer in Jesus does not guarantee a “cushy” life. Paul seemed to relate that the physical pain he endured was nothing compared to his concern for the spiritual.

Some may ask, 'If Paul had the spiritual gifts of healing and miracles, why did he not heal himself?"

If Paul had healed himself from the injuries that resulted from the beatings, scourging, stoning, etc and had gone to these groups of people with no outward signs of the injuries might that have destroyed his credibility with them?  Might they have thought Paul was lying about the punishments he received?  Might this have destroyed or compromised Paul's testimony?   They saw Paul in an injured and painful body still testifying in salvation through Jesus, in spite of his suffering.

“…caught up to the third heaven…”
This may have happened when Paul was stoned and disciples gathered around him.  The first heaven contains clouds and air. The second heaven contains stars and sky. The third heaven is where God lives, where His glory shines. See the firmament in Genesis.

The natural response to this experience would be pride. No one else experienced this so Paul was given a thorn in the flesh. Any handicap we might live with can be our "thorn in the flesh". Satan wanted this to turn Paul. God wanted to humble Paul. Pride doesn’t usually exist in people of pain. It is not always God's will to keep us from pain and pressure. Remember that suffering is not new. Pride comes with achievement. Contentment does not require comfort.

“…a thorn in my flesh, a messenger of Satan, to torment me.”
Many scholars have done extensive research in an attempt to discover what this “thorn” in the flesh was and no one can say for sure. But whatever it is, the most important thing is that Paul accepts this and even boasts about this weakness. Rejoice and be glad to be found worthy to suffer for the cause of Christ.