Frank Viola has revived and refined a theory of some of the Church Fathers that Paul’s “thorn in the flesh” in 2 Corinthians 12:7 refers to his opponents. Only Viola goes one step further in thinking Paul may have meant just one person, “a messenger from Satan.”
His reference to Numbers 33:55, where Numbers calls people who vex you “thorns in the side”, is persuasive.
He goes back to the so-called Judaizers who opposed Paul in Galatia. He adopts F.F. Bruce’s understanding that the Galatians were from south Galatia and that the letter to them was one of Paul’s earliest. I don’t find that persuasive. But I don’t think it matters. Even on the old theory of F.C. Bauer, that Peter (! ) was Paul’s main opponent, this theory would still work.
I wonder if Paul thought of a person, but an angelic one (in other words, a demon), as his thorn in the flesh. His thought world was different from ours. The “one who restrains” in 2 Thessalonians 2:7 might also refer to an angel. But these are obscure texts, so we have to admit that we don’t know exactly what Paul meant.