Albert Barnes' Bible Commentary
Numbers 8:5-22
The Levites could only undertake their duties Numbers 3; Numbers 4 after the formal exchange of the Levites for the first-born Numbers 3:44.
The distinction between the “consecration” of the priests Leviticus 8 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.
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 could have been only general, but tokens of individual purification are specified (compare also Leviticus 14:8).
The two bullocks were “to make an atonement for the Levites,” and therefore are presented in their name. These offerings are similar to those prescribed in Leviticus 8:14 ff at the consecration of the priests, except that the burnt-offering was on that occasion a ram. The larger victim corresponds to the larger number of the Levites.
The children of Israel - i. e. through the heads of their tribes, who Numbers 7:2 no doubt acted for their tribesmen. This act, the distinguishing feature of the ceremony, represented the transfer to the Levites of the sacred duties originally incumbent on the whole people.
Offer ... offering - Compare the margin Aaron pointed to the Levites, and then waved his hands, indicating (compare Leviticus 7:30 note) that the offering was dedicated to God, and, again, by grant from Him, withdrawn for the use of the priests.
Make an atonement for the children of Israel - i. e. by performing those services which were due from the children of Israel; the omission of which by the children of Israel would, but for the interposition of the Levites, have called down “wrath” from God, or Numbers 1:53 “plague.” The institution of the Levites was an extension of that mediatorial system which the people themselves, terrified at the direct manifestations to them of the divine presence, desired; see Deuteronomy 5:25. Further, it is suggested to us here as an act of mercy on the part of God; yet even the priests and Levites themselves were not always sufficiently heedful and reverent. Compare Numbers 17:10; Leviticus 10:1 ff; 2 Samuel 6:6 following.
Were purified - Rather, purified themselves; as directed in Numbers 8:7.