World Wide Study Bible
a Bible passage
13. how through infirmity—rather, as Greek, "Ye know that because of an infirmity of my flesh I preached," &c. He implies that bodily sickness, having detained him among them, contrary to his original intentions, was the occasion of his preaching the Gospel to them.
at the first—literally, "at the former time"; implying that at the time of writing he had been twice in Galatia. See my Introduction; also see on Ga 4:16, and Ga 5:21. His sickness was probably the same as recurred more violently afterward, "the thorn in the flesh" (2Co 12:7), which also was overruled to good (2Co 12:9, 10), as the "infirmity of the flesh" here.