In his second letter to the Corinthians, Paul claimed that he had been caught up into paradise on a couple of occasions and seen things that he could hardly describe (2 Cor 12:1-6). He did not record them in any of letters.

Paul then explained that God gave him a “thorn in the flesh” to keep him from becoming conceited because of the greatness of these revelations. He explains that this was a messenger sent from Satan to torment him (2 Cor 12:7).

Because of the surpassing greatness of the revelations, for this reason, to keep me from exalting myself, there was given me a thorn in the flesh, a messenger of Satan to torment me—to keep me from exalting myself!
Commentators have discussed the nature of the “thorn in the flesh. Most believe that it was some physical disability. Some have suggested that Paul was short-sighted. A couple suggested that he had bad headaches. Another suggested that he was afflicted with ear infections. One suggested that he had a bad toenail infection. These commentators missed the point, because they failed to understand what Paul actually wrote.

When Paul asked for the evil spirit to be withdrawn from him, God refused, but said,

My grace is sufficient for you, for my power is made perfect in your weakness (2 Cor 12:9).
Paul understood this truth and responded by boasting about his weakness, so that the power of Jesus could rest on him. He then explains the nature of the weakness and describes how he responds.
That is why, for Christ’s sake, I delight in weaknesses, in insults, in hardships, in persecutions, in difficulties. For when I am weak, then I am strong (2 Cor 12:10).
He delights in insults, hardships and persecutions, because when they make him weak, he becomes strong in the Spirit of Jesus. But that is exactly what he had already explained that thorn in the flesh does. The weakness it causes makes him strong in Jesus.

The thorn in the flesh is the hardship, beatings and persecution that Paul experienced. A person who was radically pursuing God’s will like Paul could claim that God would protect from all trouble, but that had not happened. A spiritual power had been given authority to attack him.

Paul does not say that God sent this evil power. Rather, Paul was working in areas where the political and religious leaders had given spiritual principalities and power permission to work. By going into Asia Minor, Paul was working into enemy territory. This meant that the powers of evil had authority to stir up the political and religious leaders to attack Paul in an attempt to disrupt his message. Paul describes the nature of their attack in the previous chapter (2 Cor 11:23-25). The list of his trials is alarming.

These sufferings were caused by the spiritual powers of evil that had authority to attack him while he was in enemy territory. They did the worst they could, but the power of Jesus did even greater things Paul despite his sufferings. His mission was stopped, but was strengthened.

Why did Paul use the expression “thorn in the flesh”. When I read the list above, my first thought was that Paul experienced even worse physical sufferings than Jesus. But Paul would not want anyone to think that, so he described his suffering as a thorn in the flesh.

Jesus wore a crown of thorns. The thorns pressing into his head represented the terrible pain that he had to bear on our behalf. Paul said that his sufferings were like only one thorn pressing into his flesh, to indicate that his suffering was far less than born by Jesus.

Whereas, Jesus wore a crown of thorns, Paul was annoyed by just one trivial thorn. His trials were real, but they were minuscule compared with what Jesus carried on the cross. That's how Paul saw it anyway. An he rejoiced in his sufferings, because they allowed him to experience the power of the Spirit.

If we follow Jesus and Paul and go into enemy territory to share the gospel we will sometimes be attacked by the spiritual powers with authority in that place, as they try to hold back the gospel. However, whatever we suffer is just one thorn in our flesh. We don’t get a crown of thorns pressed onto our heads like Jesus. Better still, our sufferings release the power of the Spirit.