Albert Barnes Commentary Lamentations 4:21-22

"Rejoice and be glad, O daughter of Edom, that dwellest in the land of Uz: The cup shall pass through unto thee also; thou shalt be drunken, and shalt make thyself naked. The punishment of thine iniquity is accomplished, O daughter of Zion; he will no more carry thee away into captivity: He will visit thine iniquity, O daughter of Edom; he will uncover thy sins." — Lamentations 4:21-22 (ASV)

The prophet ends his elegy with the language of Messianic hope. The earthly king had fallen (Lamentations 4:20); but Israel cannot really perish. First, Edom, the representative of the Church’s foes, is ironically told to rejoice. Rejoice she did at the capture of Jerusalem (Jeremiah 49:7–22); but her punishment is quickly to follow.

Lamentations 4:22 states: The punishment of your iniquity is accomplished—literally, Your iniquity is ended. This is the result of Judah having borne her punishment. And as it is not just to punish twice for the same thing, Jeremiah therefore adds, He will not send you again into captivity. This does not mean that under all circumstances Judah would have immunity from exile, as that would depend upon her future conduct. Rather, it means that with her present guilt expiated, she would have nothing to fear on its account.

He will discover your sins—see the margin. As Edom rejoices when the Church is chastised, so the day of the Church’s triumph is also the day on which the wicked meet with retribution.