Jamieson, Fausset & Brown, on Heb 12:21

“And so terrible was that which was seen, Moses said: I am frighted, and tremble.”

“the sight--the vision of God's majesty. quake--Greek, "I am in trembling"; "fear" affected his mind: "trembling," his body. Moses is not recorded in Exodus to have used these words. But Paul, by inspiration, supplies (compare Act 20:35; Ti2 3:8) this detail. We read in Deu 9:19, Septuagint, of similar words used by Moses after breaking the two tables, through fear of God's anger at the people's sin in making the golden calves. He doubtless similarly "feared" in hearing the ten commandments spoken by the voice of Jehovah.”

Imported from an open dataset — not yet checked against the printed edition.