2 Corinthians 12:7-9
And lest I should be exalted above measure by the abundance of the revelations, a thorn in the flesh was given to me, a messenger of Satan to buffet me, lest I be exalted above measure. Concerning this thing I pleaded with the Lord three times that it might depart from me. And He said to me, “My grace is sufficient for you, for My strength is made perfect in weakness.” Therefore most gladly I will rather boast in my infirmities, that the power of Christ may rest upon me.

For years I used this scripture to defend sickness.
I reasoned the “thorn in the flesh” was some disease and God refused to heal Paul over it. Some believe it as an eye disease that flared up from time to time causing him pain and some disfigurement.
It dawned on me, not long ago, the key phrase is “messenger of Satan”.
The thorn in the flesh is an actual person that caused Paul problems. Perhaps he disputed with Paul or went behind him and attempted to change his work, much like what happened to the Galatians. (cf. Galatians 1:6-9)
Paul prayed for this person’s removal, which Christ denied him.
There are always those to debate you, doubt you, and talk against your faith.
Do not let them bother you.
Live your life for Jesus Christ and go about your business.
Continue to pray for others.
Keep on reading and studying His word.
Never stop telling others about His mercy and salvation.
His grace is sufficient for you.