Charles Ellicott 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)

See Exodus 19:19 (the voice of the trumpet), Deuteronomy 4:12 (the voice of the words).

Intreated.—If we hear the voice of the Lord our God any more, then we shall die (Deuteronomy 5:25; Exodus 20:19). Though God drew near to Israel, to reveal Himself, so terrible was His voice to them, so awful the penalties which set bounds to their approach to Him, that they shrank back from hearing His words.