This week's Torah reading relates how Korach, a member of the priestly tribe of Levi, rebelliously challenged the leadership of Moses and the high priesthood of Aaron.
The Midrash relates that Korach confronted Moses with several questions. One of them concerned a Mezuzah. According to Torah law every house must have affixed on its right doorpost, a Mezuzah, a small scroll of parchment containing the first two paragraphs of the Shma Yisroel. Korach demanded of Moses: "Does a house filled with scrolls of the Torah require a Mezuzah?" Moses replied that the contents of the house were immaterial; a "Mezuzah" was required on every doorpost.
What is the logic of Moses' reply to Korach? A Mezuzah, after all, contains only two portions of the Torah. Why indeed should a house full of scrolls of the entire Torah require a Mezuzah? And what if one has a Mezuzah in a beautifully ornamented case lying on his shelf; why is this not good enough? What is the significance of having a Mezuzah nailed to the doorpost?
The answer is that although the bookshelves of a house may be filled with Torah scrolls or other holy books, this may not ensure the religious behavior of its inhabitants. It is the Mezuzah on the door which symbolizes the active awareness of G-d's presence.
The Mezuzah is placed on the doorpost, where one enters his home and leaves it. Symbolically, we takes its teachings of G-d with him wherever he goes. Our Torah is not consigned to a bookshelf, to a place of study alone, to an intellectual exercise. It is a factor in his life at all times, and all his actions are guided by the realization that... "The L-rd our G-d is One," as written in the Mezuza.
We are told of someone boasting to his Rabbi about all the Torah he had learned and mastered. The Rabbi replied, "You tell only of the Torah that you have learned, but what has the Torah taught you? Ask not, 'How much Torah knowledge have I acquired?' Ask rather, 'How much has Torah trained, educated and refined me?'"