John Calvin Commentary Lamentations 4:12

"The kings of the earth believed not, neither all the inhabitants of the world, That the adversary and the enemy would enter into the gates of Jerusalem." — Lamentations 4:12 (ASV)

He confirms the same point; for when something unbelievable happens, either we are extremely stupid, or we must be moved and affected. The Prophet, therefore, now says that the destruction of the city of Jerusalem had been unbelievable, because God had defended it by his power. It was also so fortified that no one believed it could be captured, and the grandeur of the city was known everywhere.

He then says that Jerusalem had been captured and overthrown, which none of the pagans—neither their kings nor their people—had thought possible.

It therefore follows that the city had been destroyed by God’s hand rather than by the power of enemies. Nebuchadnezzar had indeed brought a strong army, but the city was so well fortified that they thought all attempts would be in vain.

Therefore, that the city was captured and demolished could not be attributed to human forces, but to a power hidden from human eyes. It therefore follows that it was God’s work, and indeed unique.

We now, therefore, understand the Prophet's purpose in saying that neither kings nor people believed that enemies could storm Jerusalem. He then adds: