Charles Ellicott Commentary Exodus 19:9

"And Jehovah said unto Moses, Lo, I come unto thee in a thick cloud, that the people may hear when I speak with thee, and may also believe thee for ever. And Moses told the words of the people unto Jehovah." — Exodus 19:9 (ASV)

And the Lord said... — The first step in the great event of the formation of a covenant between God and Israel was completed by the people’s acceptance of God’s offer. The second step was now to be taken. The terms of the covenant must be declared, and it pleased God to declare them, or, at any rate, the most important and fundamental of them, in the hearing of the people. He therefore makes the announcement of His approaching manifestation of Himself, and proceeds to give directions connected with it to Moses.

Lo, I come unto thee in a thick cloud. —Hebrew, in the denseness of a cloud. Though God is light—or rather, because He is light, clouds and darkness are round about Him (Psalms 97:2). Even when He reveals Himself, He still dwells in the thick darkness (2 Chronicles 6:1). It is absolutely necessary that He should be closely veiled when He draws near to men, for otherwise they could not endure for a moment the brightness of His presence. (2 Chronicles 5:14; 2 Chronicles 7:2).

If even the light that remained on Moses’ face after speaking with God required him thereafter ordinarily to wear a veil before the people (Exodus 34:33–35), how much more necessary must it be that God should cover His face when He condescends to converse with men! In the present case, it would seem to have been the pillar of the cloud that had guided Israel, which served Him for a covering, and out of which He spoke to Moses and the people.

That the people may hear... and believe thee for ever. —God’s purpose in manifesting Himself to the people was twofold:

1. To impress them with the awful sense of His presence, and through them, their descendants;
2. To make them more ready to submit to Moses, and believe him for ever.

On the whole, it must be said that the purpose was accomplished. God has remained to the Israelites, for more than three millennia, an awful power, real, personal, tremendous. The Law of Moses, under whatever false interpretations, has remained the guide of their life. Though the living Moses was often resisted and despised, the dead Moses has been reverenced and obeyed from his death to the present time. His laws are still accepted and professedly obeyed by the entire Jewish community.