Adam Clarke on Exodus 19:16

Thunders and lightnings, and a thick cloud - and the voice of the trumpet - The thunders, lightnings, etc., announced the coming, as they proclaimed the majesty, of God. Of the thunders and lightnings, and the deep, dark, dismal, electric cloud, from which the thunders and lightnings proceeded, we can form a tolerable apprehension; but of the loud, long-sounding trumpet, we can scarcely form a conjecture. Such were the appearances and the noise that all the people in the camp trembled, and Moses himself was constrained to say, "I exceedingly fear and quake," Heb 12:21. Probably the sound of the trumpet was something similar to that which shall be blown by the angel when he sweareth, by Him that liveth for ever, There shall be time no longer!