Keilim, Chapter 9, Mishnah 2. At the end of the previous mishnah we were told in passing that a metal utensil resting inside a sealed earthenware vessel does not enjoy that vessel's protection and contracts tumah. Our mishnah returns to that halachah, spells it out and shows where it came from: originally it was disputed, with Beit Shammai on one side and Beit Hillel on the other.
The background is the law of tzamid patil. An earthenware vessel that is closed with a tight seal forms a barrier against the tumah of a corpse. When such a vessel stands under the same roof as a met, the tumah does not penetrate the seal, and whatever is inside remains tahor by Torah law. Our mishnah asks whether that protection extends to everything inside the vessel without exception.
The Case of the Mishnah
"Chavit shehi mele'ah mashkin tehorin": an earthenware barrel is filled with liquids that are tahor. "Umeneket betocha": inside the barrel there is a meneket, a metal pipe or tube of the sort used for drawing liquids out. "Mukefet tzamid patil": the barrel is closed with a tight seal all around. "Unetunah be'ohel hamet": and the barrel is placed in a tent, or under a roof, together with a corpse.
The barrel itself and its liquids are clearly the ordinary case of a sealed earthenware vessel. The question is the metal pipe: how do we treat a utensil that is not earthenware when it is lying inside a sealed earthenware barrel?
Beit Shammai and Beit Hillel
Beit Shammai's ruling is stated as "hachavit vehamashkin tehorin, umeneket tme'ah." In their view the barrel and its contents of liquid stay tahor, for the tight seal keeps out the tumah that fills the tent. The metal tube, though, contracts tumah from the met, notwithstanding the fact that it lies within the sealed barrel. As a matter of Torah law, a properly sealed earthenware vessel guards everything it contains without distinction; what Beit Shammai are teaching is a rabbinic enactment, that earthenware safeguards only earthenware and that its seal does not confer protection on utensils fashioned from other materials.
Beit Hillel answer with two words: "af meneket tehorah." The tube, they hold, is tahor no less than the rest of the barrel's contents, since it too lies behind the seal. As they see it, nothing warrants an enactment restricting a sealed vessel's protection to items of earthenware alone, and consequently there is no cause to separate the tube from the barrel and its liquids and treat it more stringently.
Beit Hillel Retract
The mishnah's final clause records what happened afterward. Beit Hillel came to know of the position taught by Beit Shammai, and they abandoned their own: "chazru Beit Hillel," they went back, "lehorot kedivrei Beit Shammai," to issue rulings in accordance with Beit Shammai. From then on the accepted halachah was that by rabbinic enactment a tube, and likewise any utensil whose material is not earthenware, gains nothing from the seal on the barrel and becomes tamei from the corpse for the very reason that it is not made of earthenware.
Why the Decree Was Made
The purpose of the decree touches on the relationship between two kinds of people. A chaver is someone reliable, who is meticulous about tumah and taharah. An am ha'aretz is not trusted in these matters. The Sages wanted to limit the extent to which a chaver would be influenced by an am ha'aretz and would find himself involved with his utensils.
The worry was that an am ha'aretz would claim without hesitation that his earthenware container had been properly sealed, never realizing that his word was not being accepted. Once the Sages legislated across the board that a seal on earthenware confers no protection on anything made of another material, the dynamic shifts. Nobody is being singled out, since the identical rule governs every person alike. Precisely because the halachah is uniform and open, the am ha'aretz has no reason to be defensive and speaks candidly about the contents of his vessels.
There is a good deal more detail behind the reasoning of this decree, but the bottom line of our mishnah is clear: Beit Hillel came to accept the decree of Beit Shammai, and the halachah follows it.