This is what you must do to cleanse them: Sprinkle them with the water of purification. Have them shave their whole bodies and wash their clothes, and so purify themselves.
7. And thus shalt thou do unto them. Aaron is commanded first to sprinkle the water of purifying upon them, to cleanse them from their uncleanness; and not only so, but they are commanded to wash their clothes, that they may diligently beware of any impurity being anywhere about them, whereby their persons may be infected.
We read before of the separating of the Levites from among the children of Israel when they were numbered, and the numbering of them by themselves (Num 3:6, Num 3:15), that they might be employed in the service of the tabernacle. Now here we have directions given for their solemn ordination (Num 8:6), and the performance of it, Num 8:20.
Commenting on Numbers 8:5-26
And thus shall thou do unto them, to cleanse them,.... Or order Aaron to do unto them; the cleansing of the Levites was the work of Aaron, either by himself or by his order; in which he was a type of Christ, who is the refiner and purifier of the sons of Levi, Mal 3:3, sprinkle water of purifying upon them; or "water of sin"...