John Gill Commentary Hebrews 12:19

"and the sound of a trumpet, and the voice of words; which [voice] they that heard entreated that no word more should be spoken unto them;" — Hebrews 12:19 (ASV)

And the sound of a trumpet
(Exodus 19:16Exodus 19:19) (20:18) , which made it still more awful, as the sound of the trumpet will at the last day:

and the voice of words ;
of the ten words, or decalogue; which was as an articulate voice, formed by angels; and, therefore, the law is called the word spoken by angels, (Hebrews 2:2) and is represented, as the voice of God himself, (Exodus 20:1) who made use of the ministry of angels to deliver the law to Moses; "which" voice is called (Myrbd lwq) , "the voice of words", in (Deuteronomy 4:12) , and this voice,

they that heard, entreated that the word should not be spoken to
them any more :
fearing that they should die; wherefore they desired Moses to be their mediator, and draw nigh to God, and hear his words, and speak them to them, from him, (Exodus 20:19) (Deuteronomy 5:24–27) .