Paul's "thorn". I found this commentary here (Emphasis in bold is mine)
Paul speaks of a “thorn in the flesh” in 2 Corinthians 12:7. He calls it “a messenger of Satan” that had a purpose of “torment.” Many explanations have been put forward, but whether Paul is referring to a physical, spiritual, or emotional affliction—or something else entirely—has never been answered with satisfaction. Since he was not talking of a literal thorn, he must have been speaking metaphorically. Some of the more popular theories of the thorn’s interpretation include temptation, a chronic eye problem, malaria, migraines, epilepsy, and a speech disability. Some even say that the thorn refers to a person, such as Alexander the coppersmith, who did Paul “a great deal of harm” (2 Timothy 4:14). No one can say for sure what Paul’s thorn in the flesh was, but it was a source of real pain in the apostle’s life.
Paul clues us in concerning the thorn’s purpose: “To keep me from becoming conceited because of these surpassingly great revelations.” So, God’s goal in allowing the thorn in the flesh was to keep Paul humble. Anyone who had encountered Jesus and was commissioned personally by Him (Acts 9:2-8) would, in his natural state, become “puffed up.” Add to that the fact that Paul was moved by the Holy Spirit to write much of the New Testament, and it is easy to see how Paul could become “haughty” (KJV) or “exalted above measure” (NKJV) or “too proud” (NCV).
Paul also says that the affliction came from or by a “messenger of Satan.” Just as God allowed Satan to torment Job (Job 1:1-12), God allowed Satan to torment Paul for God’s own good purpose.
No one likes to live in pain. Paul sought the Lord three times to remove this source of pain from him (2 Corinthians 12:8). He probably had many good reasons why he should be pain-free: he could have a more effective ministry; he could reach more people with the gospel; he could glorify God even more! But the Lord was more concerned with building Paul’s character and preventing pride. Instead of removing the problem, whatever it was, God gave Paul more overwhelming grace and more compensating strength. Paul learned that God’s “power is made perfect in weakness” (verse 9).
The exact nature of Paul’s thorn in the flesh is uncertain. There is probably a good reason that we don’t know. God likely wanted Paul’s difficulty to be described in general enough terms to apply to any difficulty we may face now. Whether the “thorn” we struggle with today is physical, emotional, or spiritual, we can know that God has a purpose and that His grace is all-sufficient.
What a comfort to know that whatever we are going through that God is with us and that He can use a hardship in our lives for good.
Finally, brothers, rejoice. Aim for restoration, comfort one another, agree with one another, live in peace; and the God of love and peace will be with you.
Paul's closing words to the Corinthians can be compared to Christ's instructions as we await his return:
Rejoice - the battle has already been won and God is victorious. Aim for restoration - forgive because you are forgiven. Comfort one another - Love your neighbour as yourself and take care of their needs. Agree with one another- do not stir up anger and cause divisions with others. Live in peace- Live as Jesus did. the God of love and peace will be with you - The Holy Spirit
Christianity is more than believing God exists. Even Satan acknowledges God. When we fail to live our lives for God and within His plan, we become foolish. We may not even fully comprehend how our foolish thinking can deny our eternal salvation. We rely on ourselves instead of God. That is a recipe for disaster.
Just like the gift of salvation is for everyone, so is the accountability for our actions. One day we will all have to give an account before God. No matter what "thorns" we endure. Not matter what happens in our lives while we wait for Christ's return. We all will face judgement.
From this commentary:
Tomorrow's Bible In a Year Passage: Romans 3-7