Parah, Chapter 7, Mishnah 5. This chapter is occupied with a single principle: one who draws water for the chatas, the purifying waters of the parah adumah, may not busy himself with any other melachah from the moment he begins until the ashes are placed in the water. Our mishnah takes that principle and applies it to a very ordinary scene: a man standing at the spring who wants water both for the mitzvah and for himself.
The wording runs "Hamemaleh lo ulechatas", a man who comes to the spring with two purposes at once, the chatas on one side and his own household needs on the other. For him the ruling is "memaleh es shelo techilah vekoshro ba'asal": the ordinary water is drawn at the outset and that jug is bound onto the shoulder pole. Only then, "ve'achar kach", does he draw "es shel chatas", the water set aside for the mitzvah.
The asal is the pole laid across the shoulder from which the pitchers hang. The order the mishnah prescribes is not a matter of neatness; it is a matter of avoiding melachah at the wrong moment. Drawing water for one's private needs is itself an ordinary act of labor. If it is done first, and the pitcher is secured to the pole first, then once he turns to the water of the chatas there is nothing left to occupy him, and the mitzvah water is drawn and carried with undivided attention.
Reverse the order and the water is lost: "Ve'im milei shel chatas techilah ve'achar kach milei es shelo, pasul." If he filled the chatas water first and then drew water for himself, it is invalid. His personal drawing has wedged itself in between the filling of the chatas water and its sanctification with the ashes, and that intervening labor disqualifies the water. Had he arranged matters the other way, as the mishnah instructed, no melachah would have come between the drawing and the sanctifying, and the water would be fit.
The mishnah continues with the question of where each pitcher rides: "Nosen es shelo le'achorav veshel chatas lefanav." He places his own water behind him and the chatas water in front of him. The reason is guarding. Water of the chatas requires watching, since without supervision it can easily be rendered unfit, and a pitcher hanging behind a man's back is a pitcher he cannot see. What is in front of his eyes is under his care.
Hence the mishnah's verdict: "Ve'im nasan" the jug "shel chatas le'achorav, pasul". Slung at his back, the mitzvah water is disqualified, for water hanging where its bearer cannot lay eyes on it has not received the watching that it requires.
The closing clause turns to a traveler whose two jugs are both filled with mitzvah water: "Hayu sheneihem shel chatas". Here he may hang "echad lefanav" and "echad le'achorav", and the verdict is "kasher, mipnei she'i efshar": both are fit, since no alternative exists. A shoulder pole must balance its load, and no man can rig two vessels upon it so that both hang before his face.
Some explain this along the following lines. The requirement of guarding the water is itself from the Torah, but the further refinement that the guarding be accomplished by placing the pitcher in front rather than behind is a rabbinic stringency. The Sages did not impose that stringency in a situation where compliance is impossible, where by the nature of the pole one vessel must ride in the rear.
A second approach vocalizes those last words otherwise, reading not she'i efshar but "mipnei she'efshar": the arrangement holds not for lack of any better option, but because keeping watch over the rear jug lies fully within his reach. Both vessels hang from the single pole resting on his shoulder, so the eye he keeps on the one ahead of him covers the one at his back as well. This reading also sharpens the earlier disqualification: a man who slings his household water where he can see it and the mitzvah water out of sight has let his own errand claim his attention and pushed the chatas water from his mind. Guarding it properly lay well within his power, and having chosen an arrangement that did not, he forfeits the water.
The lesson of the mishnah is the discipline of sequence and attention. The same trip to the spring, with the same two pitchers and the same pole, is either a mitzvah performed or a mitzvah forfeited, depending on what a man does first and where he keeps his eyes.