John Calvin Commentary Deuteronomy 4:11

"And ye came near and stood under the mountain; and the mountain burned with fire unto the heart of heaven, with darkness, cloud, and thick darkness." — Deuteronomy 4:11 (ASV)

And you came near and stood. This explanatory narrative is intended to prove the same thing, namely, that Moses was only the ambassador and minister of God, because the mountain burned in the sight of all the people, so that God might be manifested, speaking from the midst of the fire.

His statement that they only heard the voice, but saw no similitude, may be understood as a kind of admission, (concessionis.) Thus, the two clauses would be read adversatively: “Although no similitude appeared, yet a voice penetrated even to your ears.” But I believe this was expressly stated more clearly to show that it was the voice of God, and not proceeding from a human being. For no one could have so concealed himself by artifice as to prevent himself from being seen speaking; in contrast, they witnessed the voice emerge from the fire without any external agency.