The punishment of your iniquity, O daughter of Zion, is accomplished; he will keep you in exile no longer; but your iniquity, O daughter of Edom, he will punish; he will uncover your sins.
This verse, in my judgment, is incorrectly explained; and the Jews have toiled much, for there seems to be a kind of inconsistency, since it is certain that they were afterwards scattered into exile, not only once, but several times. Hence they interpret this place of the second dispersion by Titus, under the authority of his father Vespasian.
David's psalms of lamentation commonly conclude with some word of comfort, which is as life from the dead and light shining out of darkness; so does this lamentation here in this chapter. The people of God are now in great distress, their aspects all doleful, their prospects all frightful, and their ill-natured neighbours the Edomites insult over them and do all they can to exasperate their destroyers against them.
Commenting on Lamentations 4:21-22
The punishment of thine iniquity is accomplished, O daughter of Zion,.... In part in the seventy years' captivity in Babylon, and more fully in their present captivity; for, as has been observed, there are some things in the preceding account, which had a further accomplishment in the destruction of Jerusalem, and the distress of the Jews by the Romans.