John Calvin Commentary Jeremiah 51:40

"I will bring them down like lambs to the slaughter, like rams with he-goats." — Jeremiah 51:40 (ASV)

This is a comparison different from the former, when the Prophet said that they would be like lions, but only regarding their roaring. But He now shows how easy that ruin would be when it pleased God to destroy the Babylonians. Concerning their cry, they were like lions; but concerning the ease of their destruction, they were like lambs led to the slaughter. God does not mean here that they would be endowed with so much gentleness as to give themselves up to a voluntary death; rather, He means that however strong the Babylonians might have been previously, and however they might have threatened all other nations, they would then become faint-hearted and be led to the slaughter as if they were lambs or rams.

This is a comparison that often occurs in the prophets, for sacrifices were made daily then; and the prophets then considered the destruction of the ungodly as a kind of sacrifice. For just as sacrifices were offered under the Law as evidence of piety and worship, so when God appears as a judge and takes vengeance on the reprobate, it is as if He erected an altar and thus showed evidence of the worship that is due to Him. For His glory and worship are honored, indeed, and celebrated by such sacrifices. Therefore, the destruction of all the ungodly, as we have said, can justly be compared to sacrifices, for in such instances the glory of God shines forth, and this especially belongs to His worship.