Numbers 3:41 - Ellicott's Commentary On The Whole Bible

And thou shalt take the Levites for me (I am the Lord)... — Or, And thou shalt take the Levites for Me — for Me, Jehovah. The assertions which have been frequently made respecting the transference of the priesthood of the firstborn to the Levites appear to be altogether without foundation. For (1) the priesthood which was exercised in patriarchal times was not restricted to the firstborn, but appears to have been common to the head of every family. (2) This priesthood was exercised previously to the exodus, and consequently previously to the command given to Moses to sanctify the firstborn. And (3) the priesthood, which belonged not to the firstborn exclusively, but to the Israelites at large, was thenceforth strictly confined to the family of Aaron, who inherited it not as the substitutes of the firstborn, but in the place of the whole nation.