Leviticus 27:27 - Ellicott's Commentary On The Whole Bible

And if it be of an unclean beast. — That is, if he vows the firstling of an unclean beast he could redeem it according to the valuation of the priest with the addition of one-fifth over and above the fixed value. If he did not redeem it the treasurer of the sanctuary sold it to anyone who liked to buy it at this valuation, and the proceeds were devoted to the maintenance and repairs of the sanctuary. As this is at variance with the law laid down in Exodus 13:13; Exodus 34:20, where it is enacted that the firstborn of an ass is either to be redeemed with a sheep, or is to be put to death, the authorities during the second Temple interpreted the precept in the passage before us as not applying to the firstborn of the unclean animals, but to unclean animals generally which are dedicated for the repairs of the sanctuary.