Adam Clarke on Lamentations 3:66

Persecute and destroy them - Thou wilt pursue them with destruction. These are all declaratory, not imprecatory.

From under the heavens of the Lord - This verse seems to allude to the Chaldaic prediction, in Jer 10:11. By their conduct they will bring on themselves the curse denounced against their enemies.

The Septuagint and Vulgate seem to have read "From under heaven, O Jehovah:" and the Syriac reads, "Thy heavens, O Jehovah!" None of these makes any material change in the meaning of the words.

It has already been noticed in the introduction, that this chapter contains a triple acrostic, three lines always beginning with the same letter; so that the Hebrew alphabet is thrice repeated in this chapter, twenty-two multiplied by three being equal to sixty-six.