Hayom Yom: Tevet 11

Man's life is dependent on the air around him. Without air he cannot live and the quality of life is dependent on the quality of air. In an atmosphere of Torah and mitzvot there is healthy life. In a G-dless environment life is diseased, and one is constantly threatened with the possibility of being stricken with contagious maladies. The first general step in healing is to purify the atmosphere. Purification of the air is the task of every person familiar with Torah and Torah-literature, and is effected through the letters1 of Torah. When reciting words of Torah while in the store or walking in the street or riding the subway, one cleans the air. Everyone knowledgeable in Torah must have some Torah memorized - Chumash, Tehillim, Mishna, Tanya, etc., so that at all times and in all places he will be able to think and utter the holy letters of Torah.2