Midrash su Numeri 5:2

"Command": The command is immediately, for present performance and for future generations. You say thus, but perhaps it is only for future performance! It is, therefore, (to negate this) written "Command the children of Israel that they send … (Bamidbar 19:4) "And the children of Israel did so, sending them outside the camp" — whence we derive that the command is for immediate performance. And whence do we derive that it is (also) for future generations? From (Vayikra 24:2) "Command the children of Israel that they take to you clear olive oil … (3) … an eternal statute for your generations." — But how do we derive (the same) for all the commands in the Torah? R. Yishmael says: Since we find unqualified commands in the Torah, and one of them was qualified as being for present performance and for future generations, we derive the same for all the mitzvoth in the Torah. R. Yehudah b. Bethira says: "command" in all places connotes impulsion (to the act), as it is written (Devarim 3:28) "And command Joshua and strengthen him and fortify him" — whence we learn "We strengthen only the (internally) strengthened," and "We impel only the (internally) impelled." R. Shimon b. Yochai says: "Command" in all places entails expense, as it is written (Vayikra 24:2) "Command the children of Israel that they take to you pure olive oil," (Bamidbar 35:2) "Command the children of Israel that they give to the Levites from the inheritance, etc." (Bamidbar 28:2) "Command the children of Israel and say to them: My offering, My bread, for My fires" — whence we see that "command" in all places entails expense. Except in one; and which is that? (Bamidbar 34:2) "Command the children of Israel and say to them: When you come to the land of Canaan, etc." — where the intent is: Impel them to the division of the land. Rebbi says: "Command" in all places is exhortation, as it is written (Bereshit 2:16-17) "And the L-rd G-d commanded (i.e., exhorted) the man, saying … but of the tree of knowledge of good and evil, you shall not eat."

(Bamidbar 5:2) "that they send out of the camp": I understand this to mean from the Levite camp alone. Whence do I derive that the Israelite camp is also meant? From (Bamidbar 5:3) "Outside the camp shall you send them." (Bamidbar 5:3) "and they shall not make unclean their camps in whose midst I dwell": This is the camp of the Shechinah. — But even if this were not mentioned, I could derive it a fortiori, viz. If those with dead-body tumah are ejected from the less stringent camp, that of the Israelites, how much more so are they ejected from the more stringent camp, that of the Shechinah. If so, why is "and they shall not make unclean their camps" needed? To teach that we do not punish by an a fortiori argument. R. Yehudah says: There is no need (for the verse to teach that they are sent out of the camp of the Shechinah), for it follows a fortiori, viz.: If those with (dead-body) tumah are ejected from the less stringent camp, (that of) the ark (i.e., the camp of the Levites), how much more so are they ejected from the more stringent camp, (that of) the Shechinah, (R. Yehudah obviously holding that we do punish by an a fortiori argument). If so, why is it written "and they shall not make unclean their camps?" Because from "they shall send out from the camp every leper and every zav and every tamei meth," I would understand that they are all sent to one place; it is, therefore, written in respect to a leper (Vayikra 13:46) "Solitary shall he sit" — that no other unclean ones sit with him. I might then think that zavim and the tamei meth are sent to one camp; it is, therefore, written "and they shall not make unclean their camps" — to assign a separate camp for each. These are the words of R. Yehudah. Rebbi says: There is no need (for the above). A leper was included in the general category (of the unclean), and left the category (for special mention) to teach concerning the category, viz.: Just as a leper, whose tumah is most stringent — his sending is more stringent than that of his neighbor, so, each one whose tumah is more stringent, his sending is more stringent than that of his neighbor.

This is the source for the sages' gradations of partitions (mechitzoth). Wherever zav confers tumah, metzora (leper) confers tumah. metzora is of greater stringency (than zav) in that it confers tumah upon one who enters (a house afflicted with tzara'ath [viz. Vayikra 14:46] [— wherefore a metzora is sent out of all three camps]). Wherever tamei meth confers tumah, zav confers tumah. zav is of greater stringency (than tamei meth) in that it confers tumah under an even mesama (a stone beneath which there is a cavity [viz. Vayikra 15:9] [— wherefore a zav is sent out of two camps]). Wherever tvul yom (one who has immersed in the daytime [pending purification in the evening]) confers tumah, tamei meth confers tumah. tamei meth is of greater stringency (than tvul yom) in that it confers tumah upon a man (who touches him, viz. [Bamidbar 19:22] [— wherefore a tamei meth is sent out of one camp]). Wherever one's lacking atonement (through an offering) renders (him) unfit (for eating consecrated food) tvul yom renders (him) unfit. tvul yom is of greater stringency (than one's lacking atonement) in that he renders terumah unfit.