When Moses came down from the mountain to the people, he consecrated them, and they washed their clothes.
The thick cloud prohibits curious enquiries into secret things and commands awful adoration of what is revealed. God comes down visibly so the people see His glory and are convinced He is among them. This honours Moses especially: when they hear God speak to him and see it with their own eyes, they will believe him forever.
AI summary
Commenting on Exodus 19:9-15
And Moses went down from the mount unto the people,.... The same day that he went up, the fourth day of the month: and sanctified the people; instructed them and ordered them what they should do for their sanctification, in order to their hearing the law from the mouth of the Lord: and they washed their clothes; as the Lord had directed Moses to enjoin...
Exo 19:10-15 God then commanded Moses to prepare the people for His appearing or speaking to them: (1) by their sanctification, through the washing of the body and clothes (see Gen 35:2), and abstinence from conjugal intercourse (Exo 19:15) on account of the defilement connected therewith (Lev 15:18); and (2) by setting bounds round the people, that they might not ascend or touch the mountain.
Commenting on Exodus 19:10-15