Ye know how through infirmity of the flesh I preached the gospel unto you at the first.
It seems probable that when Paul was blinded on the Damascus road and subsequently healed at the hands of Ananias, the healing was partial and his eyes continued to give him ongoing trouble. This is strongly hinted at in the immediate context of Gal 4:13; in v 15, Paul says that had it been possible, the Galatians would have plucked out their own eyes and given them to him. But why would they have had such an inclination unless he had difficulty with his eyes?
A further hint may be found in Gal 6:11, where (on the most probable interpretation) Paul notes the large size of the letters with which he is writing the closing section of the letter.
There are 3 accounts in the book of Acts that give an account of Paul’s healing from blindness after seeing the glorious light of Jesus Christ, chapters 9, 22, & 26. None of the accounts give mention to a partial healing & seem inconsistent with the analogy our Lord purposed saying in 26:18, “...I am sending you to open their eyes so that they may turn from darkness to light and from the power of Satan to God ...”. Upon observing in 2 Corinthians 11:23ff the partial list of affections the Apostle suffered it is anyone’s guess as to which suffering may have left him with a lasting affliction; however the mentioning of eyes being given if possible & Paul writing with his own hand in large letters, something not normal for the time with limited surface to write on, might indicate that his eyes may have suffered from the many beatings or stoning so that he would learn that God will use our weakness for His strength so that He receives the glory. In Athens, before Paul’s 3rd missionary journey that would take him through Galatia, Paul had no problem viewing all the false idols or the inscription, “To the unknown God”. I would suggest his eyes were fine following his receiving his sight from the Almighty at his conversion & perhaps from suffering for Christ bad eyesight might be one of the “marks I bear in my body” mentioned at the end of Galatians 6?
We do not know what Paul's "infirmity of the flesh" or "thorn in the flesh" was and so all suggestions are educated guesses. I understand the arguments for poor eyesight but none of the reasons advanced hold much water because each can be explained as ordinary literary devices and hyperbole.
Here is another suggestion (that is only an educated guess) based on Paul's remarks in 2 Cor 1:8-11. Paul may have suffered from sporadic bouts of depression - his remarks in 2 Cor 1:8 where he "despaired of life itself" suggests extreme mental anguish. This would be consistent his remark in 2 Cor 12:7 where he says that this was, "a thorn in my flesh, a messenger of Satan, to torment me."
This may be a question that we will need to wait for the next life in order to ask Paul himself.
The context is Paul's defense of his apostleship. If Paul is able to boast according to the standard of the flesh, then he has more reason to boast than anyone else and he begins to compile a list of reasons to prove why this is true, 11:16-28.
Beginning in verse 22, he says, "Are they Hebrews? So am I. Are they Israelites? So am I. Are they descendants of Abraham? So am I." These are all genealogical factors that he has in common with all other Jews. Then in verse 23, he begins to set forth a list of comparisons in which he is proven to excel above them all. "Are they servants of Christ? (I speak as if insane) I MORE SO; in far more labors, in far more imprisonments, beaten times without number, often in danger of death."
- “Five times I received from the Jews thirty-nine lashes.”
- “Three times I was beaten with rods, once I was stoned, three times I was shipwrecked, a night and a day I have spent in the deep.”
- “I have been on frequent journeys, in dangers from rivers, dangers from robbers, dangers from my countrymen, dangers from the Gentiles, dangers in the city, dangers in the wilderness, dangers on the sea, dangers among false brethren;
- “I have been in labor and hardship, through many sleepless nights, in hunger and thirst, often without food, in cold and exposure.”
- “Apart from such external things, there is the daily pressure on me of concern for all the churches. From 11:29 through 12:8 he stresses the fact that these are all things that Paul regards as weaknesses of the flesh. These are things that are hard to endure and that he had the right to boast in the fact that he has suffered in the flesh more than all of them. In 12:6 he says that he does not wish to boast in these things, "... but I refrain from this, so that no one will credit me with more than he sees in me or hears from me."
In verse 7, Paul gives the paramount reason for his capacity for boasting which was "the surpassing greatness of the revelations." To keep him from boasting and exalting himself in this he was given a "thorn in the flesh." The 'thorn' represents something that is external to the flesh but that is intrusive to the flesh. In spite of his petition to God to remove it, God says "My grace is sufficient for you." It is not through Paul's own power that he is able to endure these suffering that have been imposed upon his flesh (not to mention the psychological stress that accompanies these types of experiences), it was the grace of God that enabled him to endure them and to continue to preach in spite of them. The connecting statement that links all of this to gather is in verse 10 when he says, "THEREFORE." Whatever he says next is rooted in everything he has said up to this point and he connects it to the thorn that was given him. "Therefore, I am well content with weaknesses, insults, distresses, persecutions, and difficulties for Christ's sake. Why? Because "when I am weak THEN I am strong." The thorn made him weak. The grace made him strong. NOW, he is able to rejoice in his sufferings - in his thorn.
So, because of the "the surpassing greatness of the revelations," Paul was allowed to suffer all of these hardships - thorn in the flesh - in order to keep him from exalting himself. One is not so likely to be self-exalting when he is having the hide stripped from his back with a scourge or having to go hungry or floating around in the sea or having his bones broken from being beaten with rods or lying in a pit left for dead after having been stoned. God allowed these things so that Paul would learn humility in spite of the exalted status that God had granted him. Remember what God told Ananias in Acts 9:16 "I will show him how much he must suffer for My name's sake."
I know this is a very brief exegesis of this text and I certainly do not claim it to be infallible. It is possible that I have missed it but, it seems to me that Paul has been very clear in explaining the nature of the thorn that he had been given. If anyone has a better exegesis of this text than this, I am certainly open to correction.
His problem with his eyesight has been a favored speculation even among many commentators. We do know from Gal. 6:11 that Paul seems to have had some type of deficiency with his eyes but the nature of what the thorn was seems very clearly defined in the context of 2Cor. 12. Paul uses three different descriptive terms all of which refer to the same thing. He calls it a 'thorn in the flesh', a 'messenger from Satan', and 'my weaknesses'. These weaknesses are not of a singular nature. They are described as insults, distresses, persecutions, and difficulties all of which are in the plural. I do not doubt that his seeming deficiency with his eyes would certainly fall within this menagerie of weaknesses. The 'thorn in the flesh' is simply a descriptive term which he employed to describe a host of things he was called to endure for the cause of Christ. Their purpose was to keep him humble in the midst of his exalted position. It is hard to be proud and self-exalting when someone is beating the hide off of your back with a scourge or breaking your bones with rods or stoning you. These types of experiences are by their very nature, humbling.
Go back to Acts 14:19-20. After he was stoned and almost died in Lystra, he and Barnabas went to Derbe the next day, this was in the region of Galatia. That was the first time (first journey) he went to the region of Galatia which he mentioned in Galatians 4:13. If you are stoned to the point of death, you will sustain some very serious injuries and I guess it's the problem that he was referring to in Galatians 4:13. My greek is not the best but the concordance G769 used in the KJV (infirmity) refers more to weakness, lack of energy or feebleness than a specific disease. This could be the result of damages done to his body due to the stoning.