Exodus 19:14

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 them, and as he had commanded them, (See Gill on Exodus 19:10).