John Calvin Commentary Lamentations 3:64

"Thou wilt render unto them a recompense, O Jehovah, according to the work of their hands." — Lamentations 3:64 (ASV)

He adds a conclusion here. For, as I have said, he has until now been recounting the evils he suffered, along with the reproaches and unjust oppressions, so that God might be favorable to him.

This is the way to gain favor when we are wrongfully treated, for it is certain that God will sustain our cause. Indeed, God testifies that He is ready to help the miserable; it is His own particular work to deliver captives from prison, to give sight to the blind, and to help the miserable and the oppressed. This, then, is the reason why the Prophet now confidently asks God to render to his enemies their reward, according to the work of their hands.

If anyone were to object, saying that another rule is prescribed to us—namely, to pray for our enemies, even when they oppress us—the answer is this: the faithful, when they prayed in this way, were not motivated by their own violent feelings but by a pure and rightly formed zeal. For the Prophet here did not pray for evil indiscriminately against all, but against the reprobate, who were persistent enemies of God and of His Church.

He could then, with sincerity of heart, have asked God to render to them their just reward. And whenever the saints prayed in this way against their enemies, asking God to be an avenger, this principle must always be kept in mind: they did not indulge their own desires but were so guided by the Holy Spirit that moderation was combined with the fervent zeal to which I have referred.

The Prophet, then, speaking here of the Chaldeans, confidently asked God to destroy them, as we shall see again shortly. We also find the same imprecations in the Psalms, especially on Babylon: Happy he who shall render to thee what thou hast brought on us, who shall dash thy children against a stone (Psalms 137:8, 9).