19. after that I was turned, I repented--Repentance in the full sense follows, not precedes, our being turned to God by God (Zec 12:10). The Jews' "looking to Him whom they pierced" shall result in their "mourning for Him." Repentance is the tear that flows from the eye of faith turned to Jesus. He Himself gives it: we give it not of ourselves, but must come to Him for it (Ac 5:31).
      instructed--made to learn by chastisement. God's Spirit often works through the corrections of His providence.
      smote upon . . . thigh-- (Eze 21:12). A token of indignant remorse, shame, and grief, because of his past sin.
      bear . . . reproach of . . . youth--"because the calamities which I bore were the just punishment of my scandalous wantonness against God in my youth"; alluding to the idols set up at Dan and Beth-el immediately after the ten tribes revolted from Judah. His sense of shame shows that he no longer delights in his sin.

JFB.