John Calvin Commentary Jeremiah 49:21

"The earth trembleth at the noise of their fall; there is a cry, the noise whereof is heard in the Red Sea." — Jeremiah 49:21 (ASV)

The Prophet dwells at length on the same matter, which in itself is sufficiently clear. However, because it was not easy to convince the Jews about what had already been said concerning the destruction of the Idumeans, the Prophet continues on the same subject.

He then says that the earth trembled at the sound of their fall. By these words, he means that the calamity would be so great that it would terrify all neighboring countries.

Just as the earth shakes when a great mass falls, so the fall of the Idumeans, who had long gloried in their wealth, could not help but strike all their neighbors with terror. Lest the Jews should think what had been said was incredible, the Prophet says that even if the earth should tremble, God would still overthrow that nation.

He then adds, the cry of their voice was heard at the Red Sea.

This sea, now called the Red Sea, was at some distance. The word סוף, suph, properly means 'weedy,' a name given to it because of the bulrushes it produced; but the sea that is meant is what is now called the Red Sea.

I have said that the distance between these places was considerable. What the Prophet means is that the shaking of the land of Edom would be so great and so dreadful that its noise would make this sea tremble, even though it was some distance away.