John Calvin Commentary Jeremiah 51:53

"Though Babylon should mount up to heaven, and though she should fortify the height of her strength, yet from me shall destroyers come unto her, saith Jehovah." — Jeremiah 51:53 (ASV)

The Prophet again teaches us that, however impregnable Babylon might be, there was still no reason to doubt that God would be its judge; for it is by no means right to measure His power by our thoughts. And nothing hinders or prevents us more from embracing the promises of God than to think of what can be done naturally, or of what is probable. When, therefore, we consult our own thoughts in this way, we exclude the power of God, which is superior to all the means that can be used.

Therefore the Prophet says here that though Babylon ascended above the heavens and on high fortified its strength for itself, yet from me, he says, shall come wasters to it. A contrast between God and men must be understood here; for if there is a contest between men, they fight with one another; but the way of God is different, for He can thunder from heaven, and thus lay prostrate the highest mountains. So now we perceive the Prophet's purpose in saying that desolators would come from God to destroy Babylon, even if it were to ascend above the clouds.