Our focus right now is on the flesh of men -- the human body. When you get a serious thorn in your flesh, it is very unpleasant. But "thorn" is used a a metaphor by Paul for something physically painful and irritating.
“Here for this third time I am ready to come to you, and I will not be a burden to you,
For I do not seek what is yours, but you;
For the children are not responsible to save up for [their] parents
But parents for [their] children.”
Can any relate to a fathers love towards his children? It is not the children who put up for the father but the father for the children. What then if those children call you “a deceiver” after gains; “deceitful”? Was Paul saying I entrapped you with deceit?
“I will gladly spend and be expended for your souls. if I love you more, am I to be loved less? but be that as it may, I did not burden you myself; …never the less, crafty fellow that I am, I took you in by deceit. (To foster you for Christ and the adoption of sons sake)
“Certainly I have not taken advantage of you through any of those whom I sent to you…have I”
(Imo, he is asking why such accusations?
In saying “I urged Titus [to go], and I sent the brother with him. Titus did not take advantage of you…did he? Did we not conduct ourselves in the same spirit [and walk] in the same steps?” (The same steps as Christ who was rejected for your sakes?)
“For I could wish that I myself [separated] from Christ for the sake of my brethren, my kinsmen, according to the flesh for who are Israelites to whom belong the adoption as sons. “To foster”, adoption.
Then there is: though you have countless teachers…there are not many fathers.
All the above sounds like an irritating thorn, especially as far as fellowship is concerned. Even if you suffer illness…is it not more painful to be rejected when you need comfort the most?