the LORD said to Moses, “Go to the people and consecrate them today and tomorrow, and let them wash their garments
10. And the Lord said unto Moses. Before propounding His law, it is not unreasonable that God should command the people to be sanctified, lest He should cast pearls before swine, or give that which is holy unto dogs; for although by right of adoption they were holy, yet, as regarded themselves, the filthiness of their nature unfitted them for participating in so great a blessing.
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 the Lord said unto Moses,.... On the fourth day, according to the Targum of Jonathan: go unto the people; go down from the mountain, from the top of it, where he now was, to the camp of Israel, which was pitched before it: and sanctify them today and tomorrow; the fourth and fifth days of the month; that is, he was, to instruct them...