And the LORD said unto Moses, Go unto the people, and sanctify them to day and to morrow, and let them wash their clothes,
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.
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 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...