Surely redeem ... redeem - A stronger expression is intentionally used in reference to the redemption of the first-born of man than in reference to that of unclean beasts. For the rule as to the former admitted of no exception: the owner of the latter, if unwilling to redeem, might destroy the beasts. Compare the marginal references.
Related Commentaries of Numbers 18:15
Numbers 18:15
15 Every thing that openeth the matrix in all flesh, which they bring unto the LORD, whether it be of men or beasts, shall be thine: nevertheless the firstborn of man shalt thou surely redeem, and the firstling of unclean beasts shalt thou redeem.