Albert Barnes' Notes on the Whole Bible - Hebrews 12:20
For they could not endure that which was commanded - They could not sustain the awe produced by the fact that God uttered his commands himself. The meaning is not that the commands themselves were intolerable, but that the manner in which they were communicated inspired a terror which they could not bear. They feared that they should die; Exodus 20:19.And if so much as a beast touch the mountain, it shall be stoned - Exodus 19:13. The prohibition was, that neither beast nor man should touch it... read more
The Pulpit Commentary - Hebrews 12:19-21
And the sound of a trumpet ( Exodus 19:16 ) , and the voice of words ( Deuteronomy 4:12 ); which voice they that heard entreated that no word should be spoken to them more : for they could not endure that which was commanded (rather, enjoined), If even a beast touch the mountain, it shall be stoned ( Exodus 19:13 ; "or thrust through with a dart" is an interpolation in the text from the passage in Exodus): and so terrible was the sight, that Moses said, I exceedingly fear and... read more