And they said unto Moses, Speak thou with us, and we will hear: but let not God speak with us, lest we die.

Wesley's Notes

20:19 Speak thou with us - Hereby they obliged themselves to acquiesce in the mediation of Moses, they themselves nominating him as a fit person to deal between them and God, and promising to hearken to him as to God's messenger.

Jamieson-Fausset-Brown Bible Commentary

19. let not God speak with us, lest we die, &c.-The phenomena of thunder and lightning had been one of the plagues so fatal to Egypt, and as they heard God speaking to them now, they were apprehensive of instant death also. Even Moses himself, the mediator of the old covenant, did "exceedingly quake and fear" (Heb 12:21). But doubtless God spake what gave him relief-restored him to a frame of mind fit for the ministrations committed to him; and hence immediately after he was enabled to relieve and comfort them with the relief and comfort which he himself had received from God (2Co 1:4).

Matthew Henry's Concise Commentary

20:18-21 This law, which is so extensive that we cannot measure it, so spiritual that we cannot evade it, and so reasonable that we cannot find fault with it, will be the rule of the future judgment of God, as it is for the present conduct of man. If tried by this rule, we shall find our lives have been passed in transgressions. And with this holy law and an awful judgment before us, who can despise the gospel of Christ? And the knowledge of the law shows our need of repentance. In every believer's heart sin is dethroned and crucified, the law of God is written, and the image of God renewed. The Holy Spirit enables him to hate sin and flee from it, to love and keep this law in sincerity and truth; nor will he cease to repent.