Parah, Chapter 5, Mishnah 1. The Mishnah now turns to the vessels used in preparing the chatas waters, the waters into which the ashes of the Parah Adumah are placed. As we will see, the care demanded for these vessels begins long before the water is ever drawn: it begins in the potter's kiln.
The Mishnah's words: "Hameivi kli cheres l'chatas", one who carries an earthenware utensil that is to serve the chatas, "tovel v'lo al hakivshan", goes down to a mikveh and passes the night beside the kiln. Rabbi Yehuda disagrees: "af min habayis hu meivi v'kasher", such a utensil may be taken even out of the potter's home and is still valid, "shehakol ne'emanim al hachatas", since every person is believed in matters touching the chatas. As for terumah the Mishnah rules, "ubiterumah posei'ach es hakivshan venoteil", one uncovers the kiln and removes a utensil. Rabbi Shimon attaches a limit, "min haseder hasheini", only from the layer standing behind the outermost one, while Rabbi Yose holds "min haseder hashlishi", only from the third layer in.
Immersing and sleeping at the kiln
Someone who transports such a utensil, intending that spring water be placed into it and mixed with the ashes of the Parah Adumah, must first immerse in a mikveh. This is one of the distinctive features of the chatas: a person who is entirely tahor is nevertheless treated, for chatas purposes, as though tumah were clinging to him, and immersion is demanded of him.
Why must he also spend the night at the kiln, the furnace in which the earthenware vessels are fired? In order to stand guard over the vessel while it is still inside. Once the vessel has been fired it is capable of receiving tumah, and an am ha'aretz who reaches in and touches it would render it unusable for the chatas. Sleeping there ensures that no such hand comes near it.
Rabbi Yehuda: everyone is trusted
Rabbi Yehuda maintains that no such watch is required at all. The utensil may be fetched directly from the craftsman's home and used. Should the craftsman report that he kept it guarded, we rely on his report; even an am ha'aretz is taken at his word when he testifies that a utensil is tahor for the chatas. The reason lies in the overwhelming stringency that surrounds everything connected with the chatas, a stringency that inspires reverence in all people, so that nobody treats the matter casually or gives a false account of it.
A similar principle appears in the Gemara in Chagigah: all are trusted regarding the purity of wine brought for the nesachim, the wine libations, and regarding flour brought for the menachos, the meal offerings. Part of the concern behind this trust is that we do not want a person going off and building an altar of his own, or preparing a Parah Adumah for himself, because he has been turned away. The halachah in our Mishnah follows Rabbi Yehuda.
Terumah, and the rows in the kiln
Where terumah is concerned the standards are less demanding, and one may simply uncover the kiln and remove a utensil. Rabbi Shimon attaches a condition: the chaver should pass over the outermost layer of utensils standing in the kiln, since an am ha'aretz may have lifted the covering and handled whatever stood nearest the opening; he takes from the layer behind it instead. Rabbi Yose goes further and requires taking only from the layer after that, the third one in.
The halachah does not follow either of them. One may take a vessel even from the first row.
This mishnah thus sets the tone for the chapter: the vessel of the chatas is guarded from the moment it leaves the fire, and yet the very awe that the chatas inspires is itself what allows us to rely on the word of the one who guarded it.