When Moses came down from the mountain to the people, he consecrated them, and they washed their clothes.
Here, I. God intimates to Moses his purpose of coming down upon mount Sinai, in some visible appearance of his glory, in a thick cloud (Exo 19:9); for he said that he would dwell in the thick darkness (Ch2 6:1), and make this his pavilion (Psa 18:11), holding back the face of his throne when he set it upon mount Sinai, and spreading a cloud upon it, Job 26:9.
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