Numbers 8:14

“Thus shalt thou separate the Levites from among the children of Israel, etc.] By sprinkling the water of purification upon them; by offering sacrifices for them; by presenting them before the Lord, with the hands of the people of Israel put upon them; by offering and waving them before the Lord, and by setting them before Aaron and his sons, as their ministers: and the Levites shall be mine: in a special and peculiar manner devoted to his service, and by him given to his priests for that purpose; so the Targums of Onkelos and Jonathan, “and the Levites shall minister before me.””

“and the Levites shall be mine--that is, exempt from all military duty or secular work--free from all pecuniary imposition and wholly devoted to the custody and service of the sanctuary.”

“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…”

“separate: Num 6:2; Deu 10:8; Rom 1:1; Gal 1:15; Heb 7:26 and the Levites: Num 8:17, Num 3:45, Num 16:9, Num 16:10, Num 18:6; Mal 3:17 Numbers 8:15”