New Defender's Study Bible Notes
16:18 so mighty an earthquake. There have been many devastating earthquakes on earth, ever since the eruption of the primeval subterranean water channels that initiated the great Flood and the tectonic uplifts that terminated it (Genesis 7:11; Psalm 104:6-9). The global earthquake at the judgment of the sixth seal (Revelation 6:12-17) had been so severe that “every mountain and island were moved out of their places.” This earthquake, however, is far worse—so bad, in fact, that “every island fled away, and the mountains were not found” (Revelation 16:20).
16:19 cities of the nations. The destructive force of this global earthquake will be so great that, like Jericho at the shout of Joshua’s army, “the cities of the nations fell,” meaning that all their structures collapsed. Jerusalem, however, will not fall, but God will divide it through the midst of the Mount of Olives (the Valley of Kidron already divides it into two parts—note Zechariah 14:4,8) when the Lord returns to stand on the Mount of Olives. Other Old Testament prophets also foresaw this mighty earthquake (e.g., Haggai 2:6-7; Isaiah 24:17-21; Joel 3:16).
16:19 Babylon. The destruction of Babylon had also been noted in Revelation 14:8, but this particular theme is so important that John will interrupt the chronological account at this point in order to devote two entire chapters (Revelation 17 and 18) to it.
16:20 mountains were not found. The smoothing of the topography of the world in this way is in preparation for the millennial earth as well, fulfilling Isaiah 40:4-5.