Numbers 8:13

“And thou shalt set the Levites before Aaron, and before his sons, etc.] After atonement was made for them, as Aben Ezra observes; then they were presented to Aaron and his sons, to whom they were given to he their ministers, and assistants to them: and offer them [for] an offering unto the Lord: or, and “waved them”, etc. as before, that is, order them to be waved; for not Moses, but Aaron, did this, and indeed was done already; and therefore should rather be rendered, as by Bishop Patrick, after thou hast offered, or waved them.”

“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…”

“Set the Levites before Aaron - Give the Levites to them, or to their service. Unto the Lord - For to him they were first properly offered, and by him given to the priests in order to his service. Numbers 8:15”

“offer them: Wehainaphta othom tenoophath, literally, as in Num 8:11, "and thou shalt wave them for a wave-offering;" manifestly in allusion to the ancient sacrificial rite of waving the sacrifices before the Lord; and it is probable, that some significant action, analogous to the waving of the sacrifice, was employed on this occasion; for the Levites were considered as an offering to the Lord, to whose service they were wholly dedicated. To this the apostle Paul manifestly alludes, when, in writing to the Romans, he says ( Rom 12:1), "I beseech you, therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable…”