And the LORD spake unto Moses, saying,

Jamieson-Fausset-Brown Bible Commentary

11-13. I have taken the Levites, &c.-The consecration of this tribe did not originate in the legislative wisdom of Moses, but in the special appointment of God, who chose them as substitutes for the first-born. By an appointment made in memory of the last solemn judgment on Egypt (from which the Israelitish households were miraculously exempt) all the first-born were consecrated to God (Ex 13:12; 22:29), who thus, under peculiar circumstances, seemed to adopt the patriarchal usage of appointing the oldest to act as the priest of the family. But the privilege of redemption that was allowed the first-born opened the way for a change; and accordingly, on the full organization of the Mosaic economy, the administration of sacred things formerly committed to the first-born was transferred from them to the Levites, who received that honor partly as a tribute to Moses and Aaron, partly because this tribe had distinguished themselves by their zeal in the affair of the golden calf (Ex 32:29), and also because, being the smallest of the tribes, they could ill find suitable employment and support in the work. (See on [55]De 33:8). The designation of a special class for the sacred offices of religion was a wise arrangement; for, on their settlement in Canaan, the people would be so occupied that they might not be at leisure to wait on the service of the sanctuary, and sacred things might, from various causes, fall into neglect. But the appointment of an entire tribe to the divine service ensured the regular performance of the rites of religion. The subsequent portion of the chapter relates to the formal substitution of this tribe.

I am the Lord-that is, I decree it to be so; and being possessed of sovereign authority, I expect full obedience.

Matthew Henry's Concise Commentary

3:1-13 There was much work belonging to the priests' office, and there were now only Aaron and his two sons to do it; God appoints the Levites to attend them. Those whom God finds work for, he will find help for. The Levites were taken instead of the first-born. When He that made us, saves us, as the first-born of Israel were saved, we are laid under further obligations to serve him faithfully. God's right to us by redemption, confirms the right he has to us by creation.