The Mishna on today’s daf reminds us that there is an option for someone who prefers not to exchange his firstborn donkey with a lamb. According to the Torah (see 13:13; 34:20), if the donkey is not redeemed then it must be decapitated. The Mishna teaches that mitzvat ha-pediya kodemet le-mitzvat arifa – that the commandment to redeem the donkey is given preference over the commandment to decapitate the animal.
The fact that the Mishna chooses to refer to both redemption and decapitation as mitzvot leads to the conclusion that decapitating the donkey is also a Biblical commandment, and that someone who chooses that option is also fulfilling a mitzva. This, in fact, is the position taken by the Rambam in his Mishneh Torah (Hilkhot Bikkurim 12:1). The Ra’avad argues that decapitating the animal cannot possibly be a mitzva, and that destroying the donkey, which could have been used by the kohen, is wasteful and is certainly considered to be a transgression. He suggests that calling it mitzvat arifa – the commandment to decapitate – should not be taken literally, and that that expression is simply used to parallel the expression mitzvat pediya – the commandment to redeem – which is certainly a mitzva.
Commentaries on the Rambam point out that it is very difficult to imagine that an option clearly offered by the Torah should be considered a transgression, even if doing this is not the preferable choice when faced with this situation. To support their position, they point to the fact that the Mishna lists a number of other situations where the Torah offers alternatives, e.g., preferring yibum – levirate marriage – over ḥalitza, which will free the dead brother’s wife to marry whomsoever she pleases. Yet performing ḥalitza is certainly a mitzva, and, in fact, is preferred by the Mishna in contemporary times.
It should be noted that the Radbaz teaches that from a kabbalistic perspective, decapitation of the donkey should not be seen as damaging the animal, rather it should be viewed as bringing the animal to a higher level of existence.