...What he writes that his livelihood is such that he needs to run around all day, it would be correct for him to know by heart some chapters of Mishnayos and some chapters of Tanya, so that also “when you go on the way” he will be able to go over them whether in speech or at least in thought, and it is known the words of my saintly father-in-law (the sixth Chabad Rebbe) about the purification of the air through the letters of Torah and prayer...(From a letter of the Lubavitcher Rebbe King Moshiach Shlita, Igros Kodesh vol. 12, pg. 49)

Torah Words On the Go