After that I was turned - Converted from my sin, folly, and idolatry.
I repented - To conviction of sin, I now added contrition for sin. Conviction, in this sense of the word, must precede contrition or repentance. As soon as a man sees himself lost and undone, he is convicted of sin; when convicted, he begins to mourn. Thus contrition follows conviction.
I smote upon my thigh - My sorrow grew deeper and deeper; I smote upon my thigh through the extremity of my distress. This was a usual sign of deep affliction. See Eze 21:12. It was the same among the ancient Greeks. So Homer: -