Sanctify them - The injunction involves bodily purification and undoubtedly also spiritual preparation. Compare Hebrews 10:22. The washing of the clothes was an outward symbol well understood in all nations.

Sanctify them - See the meaning of this term, Exodus 13:2.

Let them wash their clothes - And consequently bathe their bodies; for, according to the testimony of the Jews, these always went together.

It was necessary that, as they were about to appear in the presence of God, every thing should be clean and pure about them; that they might be admonished by this of the necessity of inward purity, of which the outward washing was the emblem.

From these institutions the heathens appear to have borrowed their precepts relative to washings and purifications previously to their offering sacrifice to their gods, examples of which abound in the Greek and Latin writers. They washed their hands and clothes, and bathed their bodies in pure water, before they performed any act of religious worship; and in a variety of cases, abstinence from all matrimonial connections was positively required, before a person was permitted to perform any religious rite, or assist at the performance.

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 how they were to sanctify themselves in an external way, by washing themselves, as after mentioned, their bodies and clothes, and by abstaining from all sensual pleasures, lawful or unlawful:

and let them wash their clothes; which the Jews understood not of their garments, but of their bodies also; teaching them by these outward things the necessity of internal purity and holiness, to appear before God: these outward rites were in use before the law of Moses, as appears from Genesis 35:2 and the Heathens themselves have similar notions of the cleanness of bodies and garments, as well as the purity of mind, being acceptable to their deities (n).

(n) "Casta placent superis, pura cum veste venito". Tibullus.

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 Genesis 35:2), and abstinence from conjugal intercourse (Exodus 19:15) on account of the defilement connected therewith (Leviticus 15:18); and (2) by setting bounds round the people, that they might not ascend or touch the mountain. The hedging or bounding (הגבּיל) of the people is spoken of in Exodus 19:23 as setting bounds about the mountain, and consisted therefore in the erection of a barrier round the mountain, which was to prevent the people form ascending or touching it. Any one who touched it (קצהוּ, "its end," i.e., the outermost or lowest part of the mountain) was to be put to death, whether man or beast. "No hand shall touch him" (the individual who passed the barrier and touched the mountain), i.e., no one was to follow him within the appointed boundaries, but he was to be killed from a distance either by stones or darts. (יּיּרה for יוּרה, see Gesenius, 69.) Not till "the drawing out of the trumpet blast," or, as Luther renders it, "only when it sounded long," could they ascend the mountain (Exodus 19:13). היּבל, from יבל to stream violently with noise, is synonymous with היּבל קרן (Joshua 6:5), and was really the same thing as the שׁופר, i.e., a long wind instrument shaped like a horn. היּבל משׁך is to draw the horn, i.e., to blow the horn with tones long drawn out. This was done either to give a signal to summon the people to war (Judges 3:27; Judges 6:34), or to call them to battle (Judges 7:18; Job 39:24-25, etc.), or for other public proclamations. No one (this is the idea) was to ascend the mountain on pain of death, or even to touch its outermost edge; but when the horn was blown with a long blast, and the signal to approach was given thereby, then they might ascend it (see Exodus 19:21), - of course not 600,000 men, which would have been physically impossible, but the people in the persons of their representatives the elders. בּהר עלות signifies to go up the mountain in Exodus 19:13 as well as in Exodus 19:12, and not merely to come to the foot of the mountain (see Deuteronomy 5:5).

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

(e) Teach them to be pure in heart, as they show themselves outwardly clean by washing.

19:10 Sanctify the people - As Job before sent and sanctified his sons, Job 1:5. Sanctify them, that is, call them off from their worldly business, and call them to religious exercises, meditation and prayer, that they may receive the law from God's mouth with reverence and devotion. Two things particularly were prescribed as instances of their preparation. 1st, In token of cleansing of themselves from all sinful pollutions, they must wash their clothes. Not that God regards our clothes, but while they were washing their clothes, he would have them think of washing their souls by repentance. It becomes us to appear in clean clothes when we wait upon great men; so clean hearts are required in our attendance on the great God. 2dly, In token of their devoting themselves entirely to religious exercises upon this occasion they must abstain even from lawful enjoyments during these three days, and not come at their wives.

19:9-15 The solemn manner in which the law was delivered, was to impress the people with a right sense of the Divine majesty. Also to convince them of their own guilt, and to show that they could not stand in judgment before God by their own obedience. In the law, the sinner discovers what he ought to be, what he is, and what he wants. There he learns the nature, necessity, and glory of redemption, and of being made holy. Having been taught to flee to Christ, and to love him, the law is the rule of his obedience and faith.