So Moses went down from the mountain to the people and consecrated the people; and they washed their garments.
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