The mezuzah is one of the few mitzvot for which the Torah states its reward. In this case, the reward is long life for oneself and one's children:
"And you shall inscribe them on the doorposts [mezuzot] of your house and on your gates, so that your days and the days of your children may be prolonged upon the land which G‑d swore to give to your fathers for as long as the heavens are above the earth." (Deut. 11:20-21)
According to the Talmud commentary of Tosafot (Menahot 44a) and the Shulchan Aruch (Yorah Deah 284) the main function of the mezuzah is to protect the house from evil. Because of this attribute, the mezuzah has been called "the coat of arms in the knighthood of G‑d." To begin to understand the mechanism of this effect of the mezuzah, we must first delve into the concept of evil itself.
Evil was created ex nihilo just as the rest of Creation. It was not created for its own sake, however, but only as an instrument of free choice. It is tolerated to the extent that it serves this purpose.
In order to allow for the existence of beings that would not be absorbed and nullified in the Source, G‑d chose to conceal and withdraw His light to create, so to speak, a "vacuum" where created beings would feel their independent existence. This, in oversimplified form, is the fundamental concept of tzimtzum (the concealment and contraction of the primordial Divine light, which is the cornerstone of Lurianic Kabbala). The concept of tzimtzum demonstrates how a monistic creation can lead to apparent dualism. (Tanya, pg. 101)
The absence of light, of course, allows the possibility for darkness - or evil
The absence of light, of course, allows the possibility for darkness - or evil. Our task is to discover G‑d hiding, as it were, behind a veil of darkness. Rebbe Dov Ber of Mezritch once found his little son crying because, while playing hide-and-seek, he hid -- but none of the children looked for him. The Rebbe started crying himself and explained to his son that our Heavenly Father also is hiding from his children, as it is written, "You are G‑d Who hides" (Isaiah 45:15), so that they should search for Him, but no one searches!
Evil, by definition, is that which conceals the true source of existence, the Creator. The very term for evil in the Kabbala, kelipa, means shell or husk. It is something that has no independent value.
Evil was created to provide us with the freedom of choice, which is possible where there is an alternative to good available. Had there been no outer shell concealing the truth, we would be forced to obey G‑d's will. If denied free choice, we would also be denied reward.
Conversely, with no free will there is no evil. An animal killing its prey for food cannot be accused of committing an evil act since it has no choice in this matter. It was created by G‑d with a predatory instinct and no free will. Similarly, angels cannot be considered good because they, too, are denied freedom of choice. They serve their Creator because they were created to do so. Only humans possessing free will can rise above angels or fall below animals, depending upon the choices they make.
Thus we see that without evil there is no free choice, and without free choice there is no good or evil. Evil allows for the exercise of good in the same sense that a ray of light can be seen only in a cloudy sky.
Once we understand that evil must exist and that it plays a positive role in the scheme of Creation, we are confronted with another problem: If evil is the husk or the concealment of G‑dly light, where does its energy come from? What sustains its existence? The answer is, of course: The same Creator Who gives life to everything. Whereas, though, the domain of holiness receives G‑d's sustenance in abundance, the merely tolerated domain of evil is relegated to feeding on "leftovers." Kabbala calls evil sitra achra, "the other side." G‑d allows a minute amount of life-giving energy to trickle down to the "other side" in order to maintain its existence. Too much of such energy kills it completely. As the sages of the Kabbala put it, "Bright light blinds the eyes of evil forces." The intellect, particularly wisdom (called chochma in Kabbala), is the bright light that disperses darkness. That is why evil must always remain in darkness, feeding on what leaks through the small holes in the domain of holiness. The Kabbala calls a hole or an opening rah (evil) because it allows vestiges of holiness to leak through, providing the "other side" with its life force. A Jewish home is a miniature Temple, a door opening to a strange and often hostile world
Now we can understand how the mezuzah protects the house. A Jewish home, which is a miniature Temple, is a vessel of holiness. A door opening to a strange and often hostile world, to the "other side," is thus called evil. The Zohar tells us that the forces of evil dwell near the door because that is where they receive their nourishment. This is similar to pathogenic bacteria and fungi flourishing in dark places.
Containing the wisdom of absolute monotheism, "Hear O Israel, the L-rd is our G‑d, the L-rd is One," the mezuzah is the ray of bright light which blinds the evil forces, denying them the right of entry and dispersing them.
This is the mystery of the mezuzah.
Time, Space, and Soul
An additional explanation of why the mezuzah is affixed to the gates of the house can be found in one of the laws of Shabbat.
The gates of a house separate reshut ha'yahid (the private domain) from reshut ha'rabim (the public domain). On Shabbat it is forbidden to carry any object from one domain to the other. Kabbala associates reshut ha'yahid (the domain of one) with the Holy One, the Singular Master of the Universe. Reshut ha'rabim (the domain of many) represents the domain of evil - the multiplicity of the physical world that disguises and hides the underlying unity of Creation.
During the first six days of the week, we must deal with the multifarious world, albeit trying to refine and repair it, to reveal its inner unity. On the seventh day we must abstain from all creative activities to observe the holiness of the day. The Hebrew word for holiness, kodesh means literally "separated." Therefore, we observe the holiness of Shabbat by honoring that separation and not carrying an object from one domain to another.
The primary task of a Jew is to reveal hidden holiness
Sefer Yetzira (6:1) says that the entire Creation exists in three dimensions: time, space, and soul. The primary task of a Jew is to reveal hidden holiness in each of these dimensions. G‑d made it easier for us by starting off the process. He sanctified the seventh day, a point of holiness in time. He sanctified the Holy Land of Israel, Jerusalem, and the Temple Mount as areas of ever increasing holiness in space. He gave us a holy spark, "a part of G‑d from above indeed," (Tanya book II, page 5) for our souls. Utilizing all of the above, we must sanctify the rest of Creation by revealing its hidden unity.
The mezuzah combines the holiness of all three dimensions. It is affixed in space to the doorpost, the threshold of the house. As the threshold marks the transition from one domain to another, the mezuzah symbolizes motion. Zuz, the root of the word mezuzah, means "to move." Motion is the essence of time. The words shana (year) and shniya (second) come from the word shinui (change). All these words denote change or motion. Hence, the mezuzah marks holiness in time.
On the other hand, the law requires that a mezuzah be affixed only to a permanent structure. The essence of space, as opposed to time, is stillness, immobility. The immobility of the mezuzah connects it to the concept of space. Furthermore, many of the laws of mezuzah deal with its position in space, i.e., where it must be affixed, on which side of the doorpost, at which height and angle. Thus mezuzah brings holiness to the concept of space.
Finally, the mezuzah, which protects the souls of Jewish people, is ultimately connected to the concept of soul. In the text of the mezuzah scroll is written, "You shall love your G‑d with...all your soul."
So we see how the mezuzah unifies and sanctifies the three dimensions of time, space, and soul. The idea of the mezuzah unifying and sanctifying time, space, and soul is ultimately expressed in the last verse inscribed on the mezuzah itself:
"...that your [soul] days [time] and the days [time] of your children [soul] may be prolonged upon the land [space] which the L-rd swore to give to your fathers [soul] for as long as [time] the heavens [space] are above the earth."
G‑d gave His chosen people signs of this special relationship. Shabbat is a sign in time. Mezuzah is a sign in space. Brit milah (circumcision) is a sign on the level of soul. The connection between mezuzah and circumcision can be observed from the imperative recited at the brit milah ceremony, "In your blood, live."(Ezekiel 16:6) Blood appears in the Torah where the word mezuzah is first mentioned (Ex. 12:22). This is in the context of the Commandment to mark the doorposts of Jewish homes with blood of the Passover sacrifice at the time of the Exodus. Moreover, the Zohar states that "The blood was of two kinds, that of circumcision and that of the Passover lamb." The Zohar further compares the place of circumcision with the "door of the body." (Soncino Zohar, II:25b-26b) The two concepts are juxtaposed also in Gen. 18:1, describing Abraham,
...he sat [ill from his circumcision] at the door of his tent.
Thus the Zohar tells us:
Happy is the portion of Israel, for the Jewish people know that they are the sons of the Holy King, for all bear His stamp. They are marked on their bodies with the holy sign [of brit milah]; their garments bear the sign of a mitzva [of tzitzit - fringes]; their heads are stamped with the compartments of tefillin [phylacteries] with the name of their Master; their hands are stamped with the straps of holiness [straps of hand tefillin]...and in their houses they bear the stamp of the mezuzah at their doorway. Thus in all ways they are marked as the sons of the Most High King. (Zohar I:266a.)
The Talmud states that the Chanuka menora should be placed in a doorway opposite a mezuzah. In Chasidic philosophy, oil symbolizes the Jewish nation. Just as oil does not mix with other liquids, so the Jews do not mix with other nations. Samuel Heilman reports a discourse given by the Belzer Rebbe on this subject:
"Oil does not mix with any other liquid. No matter how much one tries to blend the oil with other liquids, it always remains separate." The oil, he went on to explain, represents the Jewish people who, no matter how hard some may try to mix them with others, will always remain separate, like the oil... . The light...separates us from darkness. As the light symbolically separates the sacred from the profane - the Jews from the other nations - so too the mezuzah on our doors separates and protects us. Both have stood from the beginning as signs distinguishing between Jews and others. Chanukah lights and the mezuzah both symbolize separation, and thus protect the Jewish people from corrupting foreign influences "that threaten to make us disappear." Both are..."a lamp unto my feet and a light unto my path"! (Psalms 119:105)
The mezuzah unifies and sanctifies the three dimensions of time, space, and soul
Now all the pieces of the puzzle fit together. In the dimension of time, a Jew is not allowed to carry an object from one domain to another on the Sabbath because this would violate the holiness [lines of separation] of the day. On the level of soul, a Jew is forbidden to intermarry, which would cross the line of separation between the chosen holy [separated] people and the rest of humanity, between "one nation unto G‑d" and many nations. In the dimension of space, the mezuzah stands to separate [make holy] the domain of one from the domain of many, and this demarcation should not be violated by bringing alien ideas, customs, and values into a Jewish home.
Just as Shabbat is a sanctuary in time and a Jewish soul is a miniature sanctuary in the dimension of soul, the mezuzah marks a Jewish home as a miniature sanctuary in the dimension of space. By making one's house a true sanctuary of G‑dliness, a Jew not only fulfills his or her mission in life, but helps realize the primary purpose of Creation - giving G‑d a dwelling place in the lower worlds.
Mezuzah not only stands on the border between the domains of One and many, it also points inward, toward the domain of One. This comes to teach us that while G‑d created our multifaceted world from One into many, our purpose is to elevate the physical world to bring it back, as it were, to the unity of the Creator. This reverse process of bringing many back into One is the direction in which the arrow of mezuzah points us.
In the dimension of space, the mezuzah points toward the domain of the One, singular Master of the universe; in the dimension of soul, the mezuzah points to our singular G‑dly spark; and in the dimension of time, the mezuzah points to the era of Mashiach, when the unity of G‑d will be revealed - may this happen immediately!
Our sages said, "He who is observant [of the precept of] mezuzah will merit a beautiful house." (Talmud Shabbat 23b) May we soon see in the merit of this great mitzva the rebuilding of the most "holy and beautiful House" of all, the Temple in Jerusalem, as it is written, "I shall dwell in the House of G‑d all the days of my life/ To behold the beauty of G‑d and to meditate in His Sanctuary" (Psalms 27:4) [Note: heichal, 'sanctuary' in Hebrew, has the numerical value of 65, the same as 'mezuzah'.]
[Condensed from the original article and reprinted with kind permission from B’Or HaTorah vol. X (1997), pp.109-113.]