Bamidbar 19:2
This is the law that the LORD has commanded: Instruct the Israelite people to bring you a red cow without blemish, in which there is no defect and on which no yoke has been laid.
A water prepared from the ashes of the red cow is used to purify persons who have been in contact with a corpse.
Rabbi Yehuda Leib
Scripture here makes purification depend upon the Torah, the Tree of Life. Purity derives from this tree, the opposite of the Tree of Knowledge, from which comes death, the most basic category of impurity. By means of Torah, Israel can purify themselves of this defilement. We say in our prayers, “My God! The soul you placed in me is pure.” “Pure” [referring to the neshama] means that is is not capable of becoming defiled.
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Thus it is forever: the one who studies Torah attains both soul and purity. This must be what the sages meant when they said: “There is not a single letter of Torah that does not contain the resurrection of the dead, except that we do not know how to interpret.”
Like the red cow, a correctly interpreted part of the Torah purifies.
Bamidbar 20:1
The Israelites arrived in a body at the wilderness of Zin on the first new moon, and the people stayed at Kadesh. Miriam died there and was buried there.
Rashi
Why is the section on the death of Miriam placed immediately after the section treating of the red cow? To suggest to you the following comparison: What is the purpose of the sacrifices? They effect atonement? So, too, does the death of the righteous effect atonement!
Rabbi Adin Steinsaltz dvar on this parshah is mystical, considering the significance of the death of a tzaddik, in particular Miriam. He says that the transition between this world and the next, whether through birth or death, opens up both tuma (impurity) and atonement (tahara – purity) — in other words, powerful energies are released.
The tzaddik’s death atones for the sins of the whole generation and of the whole world, because the greater and more alive the person who is uprooted from the world, the more significant the changes in purity and atonement generated by the transition are. Hence, when the tzaddik leaves the world, the breach in the partition between the worlds makes an impression, in that it changes part of the nature of the world.
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The death of a tzaddik is indeed a gloomy occurrence but, on the other hand, it is also a moment of release, of rebirth, an illumination of life. When a child is born in this world, he departs from one world and is born to another world. So, too, when a tzaddik dies, he undergoes a reverse process — he departs from this world and returns to the other world. This point creates the paradox in which tuma and atonement [tahara] coincide.
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The transition between worlds can be described by the following anecdote. A man was once very ill, and he dreamed of recovering. He dreamed that in the heavenly court, he was sentenced to return to life, and he was escorted back. On the way, his escorts found a corpse, and they forced him to enter it. He cried and wailed, as he did not want to enter the corpse. After he was forced to enter the corpse, he awoke and discovered that he had returned to life.