Parah, Chapter 3, Mishnah 7. Our perek walks through the arrangements for the parah adumah one stage at a time. By this point the cow has already left the Beis Hamikdash in the company of those escorting her, headed for Har Hamishcha, the Mount of Olives, also called Har Hazeisim, the site where the burning was carried out. This Mishnah takes up two matters: an obstacle that could arise along the way, and then one of the boldest moments in the entire avodah, when a kohen was rendered tamei on purpose right before he served.
When the parah would not move
The Mishnah opens: "Lo hayesa parah rotzah latzeis, ein motzi'in ima sh'chorah, shelo yomru sh'chorah shachatu, v'lo adumah, shelo yomru shtayim shachatu." If the parah refused to go out, one does not lead another animal alongside her to coax her forward. Animals move more willingly in company, and the natural solution would be to walk a second cow next to her. But that second cow may not be a black one, lest onlookers say that a black cow was the one slaughtered. And it may not be a second red cow either, lest people say that two cows were slaughtered. In either case the appearance of the service would be distorted in the eyes of those watching.
Rabbi Yose's reason
Rabbi Yose supplies an entirely different basis for the halachah: "Lo mishum zeh, ela mishum shene'emar v'hotzi osa levada." To his mind, the ruling has nothing to do with the mistaken impressions of spectators. It flows from the wording of the pasuk itself, which directs that she be brought out levada: on her own. Since the Torah stipulates that the parah depart unaccompanied, no second animal may walk with her, whatever conclusions bystanders might or might not draw.
The elders and the immersion chamber
The Mishnah now turns to the arrangements at the site: "V'ziknei Yisrael hayu makdimin" "b'ragleihem l'har hamishcha": the zekeinim of Klal Yisrael would set out ahead of everyone, traveling by foot, and reach Har Hamishcha, the Mount of Olives, before the parah and her escort arrived. And there, "uveis tevilah hayah sham": a structure for immersion stood ready at that spot, furnished with a mikveh for whoever would have to immerse.
Making the kohen tamei on purpose
Now comes the astonishing ruling: "Umetam'im hayu es hakohen" "hasoreif es hapara, mipnei hatzedukim, shelo yihyu omrim m'orvei shemesh hayesa na'aseis." The kohen appointed to carry out the burning was made tamei by design, and the reason was the Tzedukim: they were not to be left free to assert that this avodah is valid only when performed by someone for whom nightfall had already followed his tevilah.
Behind this stands a machlokes. Scripture assigns the gathering of the ashes to an ish tahor, a pure man. The Tzedukim took that demand at its most stringent: in their reading, a person emerges from tumah only once he has immersed and the day has come to an end, so nothing involving the parah adumah could be entrusted to anyone short of that. The chachamim held otherwise, on the strength of the mesorah they had received: a tevul yom is qualified for this. Someone who immersed during the day, though the sun has not yet set on him and his purification is therefore still incomplete, may participate in preparing the parah adumah.
To make that tradition unmistakable, the chachamim did not merely state it. They would deliberately cause the kohen to become tamei, then have him immerse in the mikveh, and then have him proceed with the service immediately, while he was still a tevul yom and before the sun had set. The service was thus performed publicly and demonstratively in exactly the manner the Tzedukim denied, refuting their claim in practice and establishing for all to see that the tradition of the chachamim is the true reading of the Torah.