Albert Barnes Commentary Hebrews 12:21

"and so fearful was the appearance, [that] Moses said, I exceedingly fear and quake:" — Hebrews 12:21 (ASV)

And so terrible was the sight, that Moses said, etc. This event is not recorded in the account of the giving of the law in Exodus, and it has been questioned on what authority the apostle made this declaration concerning Moses.

In Deuteronomy 9:19, Moses indeed says of himself, after he came down from the mountain and had broken the two stone tablets in his hand, that he was greatly afraid of the Lord’s anger because of the people's sin. He stated, I was afraid of the anger and hot displeasure, wherewith the LORD was wroth against you to destroy you.

Many have supposed that this is the passage to which the apostle here alludes. However, it is very evident that this was spoken on a different occasion from the one referred to in the passage we are considering.

That statement was made after the law was given and Moses had come down from the mountain. It was not said in response to the terrors of the scene when the law was given, but out of fear of God’s wrath against the people for their sin in making the golden calf.

I do not know how to explain this, except by the assumption that the apostle here refers to some tradition that the scene produced this effect on Moses' mind. It is not improbable in itself that Moses thus trembled with alarm , nor that the memory of it should have been passed down among the numerous traditions the Jews transmitted from generation to generation.

There must have been many things that occurred during their journey through the wilderness that are not recorded in the Books of Moses. Many of these events would naturally have been preserved in the people's memory and transmitted to their descendants. Although these truths might have become mixed with much that was legendary, it is not irrational to suppose that an inspired writer may have cited relevant and true examples from these traditions of what actually occurred.

It was one method of preserving the truth to select, from the mass of traditions that were to perish, such instances of what actually took place as would be useful in future times. The circumstance mentioned here was greatly suited to increase the impression of the grandeur and terror of the scene.

Moses was accustomed to speak with God. He had met him at the “bush” and had been spoken to by him face to face. Yet, the scenes at Horeb were so awful that even he could not bear it with composure. What, then, may we suppose was the alarm of the people, when the mind of their great leader himself was so overpowered!