This is the Torah's decree... have them bring you a completely red heifer which has no blemish..."
- Chukkas 19:2f.f.
This is the mitzvah of parch adumah (red heifer). Contact with a human corpse, or even being together with a corpse overshadowed by one cover, renders a person ritually impure. The purification procedures for such a person include his being sprinkled by the "waters of purification," which contain the specially prepared ashes of a parah adumah.
There is a profound link between the precept of parch adumah and the principle of the Messianic redemption:
For the duration of the galut, until the coming of Moshiach, all Jews are in a state of impurity caused by corpses. We no longer have ashes of a parah adumah to purify us, and new ones can be prepared only in the presence of the Sanctuary (Befit Hamikdash).
Our present impurity is not only a Halachic condition determined by legal definitions. It is also a spiritual condition, for it is sin and spiritual defilement that brought about the current state of galut "Because of our sins we were exiled from our land..."
Mitzvot signify life. To follow the Divine commandments means to attach oneself to the Almighty who gave us the Torah and mitzvot, drawing unto oneself spiritual vitality from the very Source of All Life. Thus it is written: "You who cleave unto G-d, your G-d, you are all alive today".
Sin signifies death. Sin means violating G-d's Will, rebelling against G-d. It disrupts attachment to the Creator, clogging, as it were, the very channel through which the spiritual life-force flows to man, individually and collectively. Sin thus brings about the "impurity of death."
Both the "red heifer" and the Messianic redemption effect purification. The ashes of the "red heifer" are used for removing a legal state of impurity. The redemption will purify the entire people of Israel (including those who halachically are pure) from any trace of deficiency in the bond with our Father in Heaven. One of the Messianic prophecies thus says of that time, in terms analogous to the "waters of purification" of the "red heifer": "I shall sprinkle pure waters upon you that you be purified. I will purify you from all your impurities and from all your idols!"
Maimonides cites a Mishnah with the following words: "Nine 'red heifers' were prepared from the time this precept was ordained until the Second Temple was destroyed: the first was prepared by Moses our Master, the second Ezra prepared, and there were seven from Ezra to the destruction of the Temple. The tenth will be prepared by King Moshiach - may he soon be revealed, amen, may thus be (G-d's) Will!"
(Hilchos Parah Adumah 3:4)