Charles Ellicott Commentary Exodus 19:16-20

"And it came to pass on the third day, when it was morning, that there were thunders and lightnings, and a thick cloud upon the mount, and the voice of a trumpet exceeding loud; and all the people that were in the camp trembled. And Moses brought forth the people out of the camp to meet God; and they stood at the nether part of the mount. And mount Sinai, the whole of it, smoked, because Jehovah descended upon it in fire; and the smoke thereof ascended as the smoke of a furnace, and the whole mount quaked greatly. And when the voice of the trumpet waxed louder and louder, Moses spake, and God answered him by a voice. And Jehovah came down upon mount Sinai, to the top of the mount: and Jehovah called Moses to the top of the mount; and Moses went up." — Exodus 19:16-20 (ASV)

Thunders and lightnings, and a thick cloud. —Compare with this description that of Deuteronomy 4:11-12, which is fuller in some respects: You came near and stood under the mountain; and the mountain burned with fire unto the midst of heaven, with darkness, clouds, and thick darkness. And the Lord spoke to you out of the fire: you heard the voice of the words, but saw no similitude; only you heard a voice. The phenomena accumulated to impress the people seem to have been loud thunder, fierce flashes of lightning, a fire that streamed up from the mountain to the middle of the sky, dense volumes of smoke producing an awful and weird darkness, a trembling of the mountain as by a continuous earthquake, a sound like the blare of a trumpet loud and prolonged, and then finally a clear, penetrating voice.

So awful a manifestation has never been made at any other place or time, nor will be until the consummation of all things. To regard it as a mere “storm of thunder and lightning,” or as “an earthquake with volcanic eruptions,” is to miss altogether the meaning of the author, and to empty his narrative of all its natural significance.

The voice of the trumpet. —Hebrew: a voice of a trumpet. The trumpet’s blare is the signal of a herald calling attention to a proclamation about to be made. At the last day the coming of Christ is to be announced by the trump of God (1 Thessalonians 4:16). In the Apocalypse angels are often represented as sounding with trumpets (Revelation 8:7–8; Revelation 8:10; Revelation 8:12; Revelation 9:1; Revelation 9:14, and elsewhere) when some great event is about to occur.