Editing Taharat HaAvir (Purification of the Air) (section)

== Meaning and Method of Purification ==
A person's life depends on the air in which they exist, for without air it is impossible to live. The quality and type of air a person breathes determines their health and quality of life, which also affects plants and animals. This concept parallels the spiritual realm as well—when a person lives in a place where Torah was studied and mitzvot were fulfilled in the surrounding air, it influences their personality and spiritual life, adding to their mitzvot and good deeds. Conversely, when breathing air in which sins were committed and words of heresy were spoken, a person could become spiritually sick and infected, and be negatively influenced by it.

The general and primary preventative remedy for this is to purify the air, which is incumbent upon every person who knows matters of Torah. This is accomplished by reviewing and studying Torah when in a store, walking in the street, traveling on a train, or in any other place. By reciting letters of Torah, one purifies the air. Therefore, it is the duty of every person knowledgeable in Torah to have something memorized: Chumash, Tehillim, Mishnayot, or Tanya, so that at any time and in any place, they can think about and recite the letters of Torah, thereby purifying the air.

The Gemara also contains expressions about the effect of air, such as "avira d'Eretz Yisrael machkim" (the air of the Land of Israel makes one wise) and "avir migdal meshakeach" (tower air causes forgetfulness).

Chassidim emphasize two matters that especially affect the purification of air: memorizing Tanya, which the Frierdiker Rebbe (Rabbi Yosef Yitzchak Schneersohn) compared to the revelation of Hashem on Mount Sinai during the giving of the Torah when recited while walking in the street; and memorizing Mishnayot, about which the Frierdiker Rebbe stated that by each person reviewing the amount of Mishnayot they are capable of learning by heart, they will merit greeting Moshiach.

In 5702 (1942), the Frierdiker Rebbe established the Chevrat Mishnayot Ba'al Peh (Society for Memorizing Mishnayot) as part of the activities of the Machane Yisrael organization. Its purpose was that each member would receive a number of Mishnayot by lottery, which they would need to learn by heart during the year. This way, during the year, all six orders of Mishnah would be completed by heart by all members of the society, and they would review them during all free hours to purify the air.

All Chabad Rebbes had certain Chassidic discourses that they would review several times a year in order to purify the air.