A person’s life depends upon the air around him: without air one cannot live. Moreover, the kind of air in which one lives determines the quality of one’s life. When a person lives in an atmosphere of Torah and mitzvos, his life is healthy. When he lives in an atmosphere that denies G‑d, his life is sickly and he is under constant risk of contagion.

The first, comprehensive remedy is to purify the air, and this is the responsibility of those who are educated in Torah studies. It is the letters of Torah that purify the air. When a person verbalizes words of the Torah while standing in the store, walking down the street, or riding the subway, he purifies the air. Whoever is familiar with Torah learning must have something on call that he has learned by heart, be it Chumash, Tehillim, Mishnayos, or Tanya. This will enable him to review the holy words of the Torah — mentally and verbally — at any time and in every place.