And it came to pass on the third day in the morning, that there were thunders and lightnings, and a thick cloud upon the mount, and the voice of the trumpet exceeding loud; so that all the people that was in the camp trembled.

Wesley's Notes

19:16 Now at length is come that memorable day, in which Israel heard the voice of the Lord God speaking to them out of the midst of the fire and lived, Deu 4:33. Never was there such a sermon preached before or since, as this, which was here preached to the church in the wilderness. For, the preacher was God himself, Ex 19:17, The Lord descended in fire; and Ex 19:18. The Lord came down upon mount Sinai. The Shechinah, or glory of the Lord, appeared in the sight of all the people; he shined forth from mount Paran with ten thousand of his saints, attended with a multitude of the holy angels. Hence the law is said to be given by the disposition of angels, Acts 7:53. He spake from mount Sinai, hung with a thick cloud, Ex 19:16, covered with smoke, Ex 19:18, and made to quake greatly. Now it was that the earth trembled at the presence of the Lord, and the mountains skipped like rams, Psa 114:4,7, that Sinai itself, though rough and rocky, melted from before the Lord God of Israel, Jud 5:5. The congregation was called together by the sound of a trumpet exceeding loud, Ex 19:16, and waxing louder and louder, Ex 19:19. This was done by the ministry of the angels, and made all the people tremble. The introductions to the service were thunders and lightnings, Ex 19:16. These have natural causes; but the scripture directs us in a particular manner to take notice of the power of God, and his terror in them. Thunder is the voice of God, and lightning the fire of God, proper to engage both the learning senses of seeing and hearing.

Jamieson-Fausset-Brown Bible Commentary

16. on the third day in the morning, that there were thunders and lightnings, &c.-The descent of God was signalized by every object imagination can conceive connected with the ideas of grandeur and of awe. But all was in keeping with the character of the law about to be proclaimed. As the mountain burned with fire, God was exhibited as a consuming fire to the transgressors of His law. The thunder and lightning, more awful amid the deep stillness of the region and reverberating with terrific peals among the mountains, would rouse the universal attention; a thick cloud was an apt emblem of the dark and shadowy dispensation (compare Mt 17:5).

the voice of a trumpet-This gave the scene the character of a miraculous transaction, in which other elements than those of nature were at work, and some other than material trumpet was blown by other means than human breath.

Matthew Henry's Concise Commentary

19:16-25 Never was there such a sermon preached, before or since, as this which was preached to the church in the wilderness. It might be supposed that the terrors would have checked presumption and curiosity in the people; but the hard heart of an unawakened sinner can trifle with the most terrible threatenings and judgments. In drawing near to God, we must never forget his holiness and greatness, nor our own meanness and pollution. We cannot stand in judgment before him according to his righteous law. The convinced transgressor asks, What must I do to be saved? and he hears the voice, Believe in the Lord Jesus Christ, and thou shalt be saved. The Holy Ghost, who made the law to convince of sin, now takes of the things of Christ, and shows them to us. In the gospel we read, Christ hath redeemed us from the curse of the law, being made a curse for us. We have redemption through his blood, even the forgiveness of sins. Through him we are justified from all things, from which we could not be justified by the law of Moses. But the Divine law is binding as a rule of life. The Son of God came down from heaven, and suffered poverty, shame, agony, and death, not only to redeem us from its curse, but to bind us more closely to keep its commands.