There were thunders and lightnings, and a thick cloud of smoke upon the mountain, and the voice of a trumpet exceeding loud, so that the people in the camp trembled with fear, and the whole earth quaked greatly.

This was a picture foreshadowing the time of trouble in the earth, the great shaking of the nations just before the inauguration of Messiah's kingdom and the taking unto himself of his bride for the setting up of his kingdom.

St.Paul, referring to that time, by way of comparison says: "Ye are not come unto the mount that might be touched, and that burned with fire, nor unto blackness, and darkness, and tempest, and the sound of a trumpet, and the voice of words; which voice they that heard intreated that the word should not be spoken to them any more (for they could not endure that which was commanded, And if so much as a beast touch the mountain, it shall be stoned, or thrust through with a dart; and so terrible was the sight, that Moses said, I exceedingly fear and quake)" .-- Hebrews 12:18-21.
[521]We should expect, then, an antitypical fulfillment of these conditions.

And so we do find it.

The mountains (symbolically meaning kingdoms of the world) are on fire, and there is a great tempest, and trouble, and disturbance in the earth; and so terrible is the time that men's hearts are failing them for fear of what they see coming on the earth.