(Devarim 15:20) "And if there be in it a blemish": This tells me only of an animal that was born unblemished and became blemished. Whence do I derive (the same for) one that was born blemished! From " every blemish." Whence do we derive (the same for animals that are) scrofulous, warty, scabbied, old, sick, or malodorous? From " every ." I might think that they could be slaughtered (and eaten) outside Jerusalem; it is, therefore, written "lame or blind': "lame" and "blind" were in the category (of blemished animals). Why did they leave that category (for special mention)? To make them the basis for a comparison, viz.: Just as "lame" and "blind" are distinct in being external blemishes, which do not heal, so, all (blemishes which render a bechor subject to slaughtering and eating outside Jerusalem) must be of that kind.
Sifrei Devarim 126
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