John Gill Bible Commentary

Take the Levites from among the children of Israel,.... Among whom they were mixed, as were all the tribes mixed together as Aben Ezra says, before they took their journey from Mount Sinai; however, from hence forward, they were distinguished from Israelites, as they are both in Scripture and in Jewish writings; see Ch1 9:2; though this seems to design no other but their appointment and separation to their work and service, as ministers to the priests of the Lord; and so as Aaron did not assume the honour of priesthood to himself but was called of God, the Levites did not take the honour of their office to themselves but had it by the appointment and call of God: and cleanse them; with water, by sprinkling the water of purification on them, and by washing their bodies and clothes with water; which outward washing was a sign of moral purity, which was necessary to their employment in the service of the sanctuary; for though there was no particular uncleanness on them, either ceremonial or moral, but what was common to men; yet it was proper, by such outward rites, to put them and others in mind, that they which are employed about holy things should be eminently pure and holy; and as their business was to carry holy things, to bear the sacred vessels of the sanctuary from place to place when needful, they ought of all men to be clean, Isa 52:11, and in this they were emblems of the ministers of the word, who ought to be pure, as in heart, so in life and conversation, and be examples of purity to others, Co2 6:6.