Numbers 8:5

“And the Lord spake unto Moses, etc.] the same time the order about lighting the lamps was given; and this section is joined to the former, Aben Ezra thinks, to show that Aaron employed himself in lighting the lamps, but in the rest of the services the Levites helped him, and stood before him to do what he commanded them: they were ordered to be taken and given to Aaron before; and they were numbered, and their services appointed to each division of them; and now they are ordered to be ordained and consecrated to their office: saying; as follows.”

“The Levites could only undertake their duties Numbers 3:0; Numbers 4:0 after the formal exchange of the Levites for the first-born Numbers 3:44-51. The distinction between the “consecration” of the priests Leviticus 8:0 and the less solemn “purification” Numbers 8:21 of the Levites is marked. These rites of purification are similar to those incumbent on the priests of Egypt. Numbers 8:7 Water of purifying - literally, “sin water:” i. e. water to cleanse from sin; no doubt taken from the laver of the sanctuary, which was used by the priests for purification before they went into the tabernacle to minister (compare Numbers 5:17; Exodus 30:18 ff). The “sprinkling” of so large a body of men…”

“8:5-22 The Lord prescribed the dedication and cleansing of the Levites.”

“Consecration of the Levites for their service in the sanctuary. - The choice of the Levites for service in the sanctuary, in the place of the first-born of the people generally, has been already noticed in Num 3:5., and the duties binding upon them in Num 4:4. But before entering upon their duties they were to be consecrated to the work, and then formally handed over to the priests. This consecration is commanded in Num 8:7., and is not called קדּשׁ, like the consecration of the priests ( Exo 29:1; Lev 8:11), but טהר to cleanse. It consisted in sprinkling them with sin-water, shaving off the whole of the hair from their bodies, and washing their clothes, accompanied by a sacrificial…”