What Does Exodus 19:15 Mean?

Now Mount Sinai was wrapped in smoke because the LORD had descended on it in fire, and the smoke of it went up like the smoke of a kiln, and the whole mountain trembled greatly. YHWH's descent on Mount Sinai in fire is the physical phenomenon of the divine glory's unapproachable holiness: the fire and smoke are the theophany's visual expression of the burning-unapproachable holiness that the burning bush first displayed (Exodus 3:2, "the bush was burning yet it was not consumed").

The same fire that did not consume the bush now descends on the entire mountain and produces smoke that "goes up like the smoke of a kiln": the furnace image of Sodom and Gomorrah's destruction (Genesis 19:28) applied to YHWH's descending presence.

"The whole mountain trembled greatly": the mountain itself shakes. The trembling of the people (verse 16) and the trembling of the mountain are the same response: creation trembles in the presence of its Creator.

The earthquake-element of the Sinai theophany (mountain trembling) becomes the prophetic and apocalyptic symbol for YHWH's approach: Psalm 68:8 ("the earth quaked, the heavens poured down rain, before God, the one of Sinai"), Judges 5:5 ("the mountains quaked before the LORD"), Habakkuk 3:3-6 (YHWH's theophanic march causing mountains to shatter and hills to collapse). The trembling mountain at Sinai seeds all subsequent divine-approach earthquake imagery in the canon.

Hebrews 12:26-27 explicitly connects Sinai's mountain-shaking to the eschatological shaking that is coming: "At that time his voice shook the earth, but now he has promised, 'Yet once more I will shake not only the earth but also the heavens.' This phrase 'Yet once more' indicates the removal of things that are shaken, that is, things that have been made, in order that the things that cannot be shaken may remain." The Sinai mountain-trembling is the first installment of the eschatological earth-shaking that YHWH's final approach will produce: everything that can be shaken at Sinai will be: shaken in the final theophany that produces the new creation.