And thou shalt take the Levites for me, &c.— The Levites were now to be exchanged for the first-born males of the whole nation, man for man; and the cattle of that whole tribe, instead of the firstling male cattle of the whole nation; that so the Levites and their cattle, instead of the Israelites first-born men and cattle, might be given unto Aaron and the priests, to minister unto them, Numbers 3:45. This was for the first-born males of man and beast, which the Israelites now had. All the first-born that came after this, were to be redeemed, or given to the priests.
Related Commentaries of Numbers 3:41
Numbers 3:41
41 And thou shalt take the Levites for me (I am the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel.