Thorn in the Flesh

Concise Bible Dictionary:

This was something that Satan was allowed to inflict on Paul, not because of any fault he had committed, but lest he should be puffed up on account of his having been caught up into the third heaven ({vi 29030-29033}2 Cor. 12:7-10). Apparently it was something that made him contemptible in the eyes of his fleshly opponents (see 2 Cor. 10:10; 2 Cor. 11:30; {vi 29145-29146}Gal. 4:13-14).