Adam Clarke Bible Commentary

Every firstling of an ass thou shalt redeem with a lamb - Or a kid, as in the margin. In Num 18:15, it is said: "The first-born of man shalt thou surely redeem; and the firstling of an unclean beast shalt thou redeem." Hence we may infer that ass is put here for any unclean beast, or for unclean beasts in general. The lamb was to be given to the Lord, that is, to his priest, Num 18:8, Num 18:15. And then the owner of the ass might use it for his own service, which without this redemption he could not do; see Deu 15:19. The first-born of man - shalt thou redeem - This was done by giving to the priests five standard shekels, or shekels of the sanctuary, every shekel weighing twenty gerahs. What the gerah was, see Clarke on Gen 20:16 (note). And for the shekel, see Clarke on Gen 20:16 (note). It may be necessary to observe here that the Hebrew doctors teach, that if a father had neglected or refused thus to redeem his first-born, the son himself was obliged to do it when he came of age. As this redeeming of the first-born was instituted in consequence of sparing the first-born of the Israelites, when the first-born both of man and beast among the Egyptians was destroyed, on this ground all the first-born were the Lord's, and should have been employed in his service; but he permitted the first-born of a useful unclean animal to be redeemed by a clean animal of much less value. And he chose the tribe of Levi in place of all the first-born of the tribes in general; and the five shekels were ordered to be paid in lieu of such first-born sons as were liable to serve in the sanctuary, and the money was applied to the support of the priests and Levites. See this subject at large in Num 3:12, Num 3:13, Num 3:41, Num 3:43, Num 3:45, Num 3:47-51.