“…They shall take to you a perfectly red heifer…” – Bamidbar 19:2

וְיִקְחוּ אֵלֶיךָ פָרָה אֲדֻמָּה תְּמִימָה – במדבר יט, ב

The Torah commands us to prepare the ashes of a parah adumah, a red heifer, for use in the ritual purification of people or articles that contracted impurity from a dead corpse. The Torah attributes this mitzvah to Moshe, emphasizing that Bnei Yisrael must bring the red heifer to Moshe, though the ashes were actually prepared by Elazar. Similarly, the Midrash states that Moshe alone perceived the purpose of this mitzvah (see Tanchuma, Chukas 8).

Moshe’s devotion to G-d was characterized by permanence; nothing in the world could cause his commitment to G-d to waver or weaken. As a result, everything associated with Moshe is everlasting (see Talmud, Sotah 9a). For example, the Mishkan that Moshe built was hidden away, and was never destroyed by enemy hands. Even regarding Moshe himself, the Talmud (Sotah 13b) states matter-of-factly, “Moshe never died. It is written, ‘Moshe died there’, and elsewhere it is written, ‘And he was there with G-d.’ Just as in the latter passage Moshe was standing and serving, so does the former mean that he is standing and serving.” Likewise, the ashes of Moshe’s parah adumah outlasted all the others, according to the Midrash (Tanchuma, ibid.). When ashes of a new parah adumah were made in later generations, the kohen involved in their preparation would first be purified using ashes from Moshe’s parah adumah.

This explains why the mitzvah of parah adumah, more so than any other mitzvah, is attributed to Moshe. In order for the parah adumah to remove the impurity caused by a dead corpse, it must undo to some degree the cause of this impurity—death itself. This purification was therefore intrinsically connected to Moshe, who represents permanence, perpetuity, and in fact, immortality.

—Likutei Sichos, vol. 33, pp. 127-130