The Torah towards the end of Parashat Bo (13:13) introduces the mitzva of pidyon peter chamor, which requires redeeming a firstborn donkey. When a donkey delivers its first offspring, the owner must either redeem it by paying a sheep to a kohen, or kill the donkey by breaking its neck.
The Mekhilta, commenting on this verse, notes that the Torah first presents the option of redeeming the donkey with a sheep, before allowing the option of killing the donkey. The implication, the Mekhilta writes, is that “mitzvat pediya kodemet le-mitzvat arifa” – it is preferable to redeem the animal rather than kill it. The Mekhilta then proceeds to present a “davar acher” – an alternative view: “If you do not redeem it, then break its neck; since you caused a loss to the kohen’s property, then you, too, shall incur a loss of property.” A person who refuses to redeem his peter chamor by paying a sheep to a kohen is penalized by being forced to kill the donkey. The Mekhilta adds that even after the donkey is killed, one may not derive any benefit from the carcass (such as by using the leather or feeding the meat to one’s animals), such that the owner derives absolutely no benefit at all from this animal. The Torah enacted this provision as a punitive measure of sorts, punishing the owner for refusing to pay a sheep to the kohen, who depends on gifts from the rest of the nation for his livelihood.
The question arises as to why the Mekhilta presents these two comments as two different views. The term “davar acher” is generally used in reference to two opposing statements or explanations. Here, the second remark seems to simply explain the first. After establishing that redemption is preferable to killing the donkey, the Mekhilta should simply then explain that this is because the person denies the kohen his due payment. Why does the Mekhilta introduce the second remark as a “davar acher”?
The answer, perhaps, as noted by the Maharit Algazi in his work on the Ramban’s Hilkhot Bekhorot, lies in the term “mitzvat arifa” used by the Mekhilta in the first passage. In this comment, the Mekhilta speaks of arifa (breaking the donkey’s neck) as a mitzva. Although it is the less preferred option, it is nevertheless considered a mitzva to break the animal’s neck. And herein, perhaps, lies the point of contention between the two comments of the Mekhilta. Whereas the first regards arifa as a mitzva, the second views it as a punishment. One who refuses to pay a sheep to the kohen, according to the second view, is not credited with a mitzva for breaking the donkey’s neck; this is forced upon him as a penalty for eschewing his responsibilities to the kohen.
The Mekhilta thus provides the background for a debate between the Rambam and the Ra’avad. In Hilkhot Bikkurim (12:1), writes that there is a mitzvat asei to break a firstborn donkey’s neck if one refuses to redeem it with a sheep. The Ra’avad objects to this formulation, writing that one cannot be considered to fulfill a mitzva if he withholds a kohen’s payment and instead kills his animal. These two views may likely reflect the different perspectives expressed by the Mekhilta, as to whether arifa constitutes a mitzva or a penalty.