In Masechet Menachot, there is a very rich section that deals with the laws of tefillin and mezuzah. A particular theme of interest, especially in the context of the korban Pesach, is that of the mezuzah as an object that protects the house. This idea is never stated in the Torah. To the contrary, the Torah juxtaposes the mitzvah of mezuzah with that of tefillin and of constant Torah study. The message is clear – have reminders of God all around you, think of God and God’s mitzvot, and learn Torah at all times – when you go to sleep and when you rise, when you sit in your house and when you go on a journey.
Nevertheless, given that the mezuzah is placed on the door frame, it was perhaps inevitable that it would be associated with magical powers of protection. Such certainly seems to have been the case with the blood of the pesach sacrifice brought in Mitzrayim:
And they shall take of the blood, and strike it on the two side posts and on the upper door post of the houses, in which they shall eat it… For the Lord will pass through to strike the Egyptians; and when the Lord sees the blood upon the lintel, and on the two side posts, the Lord will pass over the door, and will not let the destroyer come into your houses to strike you (Shemot 12:7, 23)
Analytically, we can of course draw many distinctions between the two cases. The blood was that of a sacrifice; there is no suggestion that it had magical powers per se, and it is God who sees the blood, not the blood which operates on its own power. Nevertheless, the reality of a wrapped parchment, probably placed in a casing, on the door frame of one’s house, combined with the parallels to the blood of the pesach, could easily suggest to the religious imagination of the masses that this mezuzah functioned like a kemiyah, an amulet, and through its “power” the house was protected. Thus, we find people who as soon as something bad happens in their house, will have their mezuzot checked. And, similarly, we find practices going back hundreds of years to write the names of angels on the backside of the mezuzah – a type of practice associated with charms and kemiyas.
This approach to mezuzah is alluded to in the gemara Menachot (33b). The Gemara gives two explanations to Rava’s statement that the mezuzah needs to be placed in the outermost tefach of the doorframe. One explanation is psychological/religious: so that a person encounters the mezuzah as soon as she steps into the doorframe. The other explanation, however, is more magical/metaphysical: “So that it will guard it [the house]” (Rashi – “[The mezuzah will guard] the entire house [starting from the very beginning of the doorframe] from demons”). This second explanation, however, seems to point to the understanding of the mezuzah as a kemiyah, an amulet which magically protects the house.
Not surprisingly, Rambam comes out strongly against this type of approach to the mitzvah of mezuzah:
… אבל אלו שכותבין מבפנים שמות המלאכים או שמות קדושים או פסוק או חותמות הרי הן בכלל מי שאין להם חלק לעולם הבא, שאלו הטפשים לא די להם שבטלו המצוה אלא שעשו מצוה גדולה שהיא יחוד השם של הקב”ה ואהבתו ועבודתו כאילו הוא קמיע של הניית עצמן כמו שעלה על לבם הסכל שזהו דבר המהנה בהבלי העולם.
… But those who write inside [the mezuzah] the names of angels or holy names or a verse or seals, such people are in the category of those who have no portion in the World to Come. For these idiots, it is not enough for them that they have [through these actions] negated a positive mitzvah [by invalidating the mezuzah], but they have turned an important mitzvah – viz., the unification of God’s name and the love of God and the worship of God – and made it like it were a kemiyah, a magical amulet, whose function is to serve their personal needs, as they tend to think in their foolish thoughts that this [mezuzah] is a thing that affords them benefit in meaningless worldly things.
Rambam, Laws of Mezuzah 5:4
Thus, when Rambam explains the religious significance of mezuzah, he focuses on the first explanation given in our Gemara, the psychological/religious one:
וחייב אדם להזהר במזוזה מפני שהיא חובת הכל תמיד, וכל זמן שיכנס ויצא יפגע ביחוד השם שמו של הקדוש ב”ה ויזכור אהבתו ויעור משנתו ושגיותיו בהבלי הזמן, וידע שאין דבר העומד לעולם ולעולמי עולמים אלא ידיעת צור העולם ומיד הוא חוזר לדעתו והולך בדרכי מישרים, אמרו חכמים הראשונים כל מי שיש לו תפילין בראשו ובזרועו וציצית בבגדו ומזוזה בפתחו מוחזק הוא שלא יחטא שהרי יש לו מזכירין רבים והן הם המלאכים שמצילין אותו מלחטוא שנאמר חונה מלאך יי’ סביב ליראיו ויחלצם,
A person must show great care in [the observance of the mitzvah of] mezuzah, because it is an obligation which is constantly incumbent upon everyone.
[Through its observance,] whenever a person enters or leaves [the house], he will encounter the unity of the name of the Holy One, blessed be He, and remember his love for Him. Thus, he will awake from his sleep and his obsession with the vanities of time, and recognize that there is nothing which lasts for eternity except the knowledge of the Creator of the world. This will motivate him to regain full awareness and follow the paths of the upright.
Whoever wears tefillin on his head and arm, wears tzitzit on his garment, and has a mezuzah on his entrance, can be assured that he will not sin, because he has many reminders. And these reminders are the true angels who will prevent him from sinning, as [Psalms 34:8] states: “The angel of God camps around those who fear Him and protects them.”
Laws of Mezuzah 6:13
Notice, also, how Rambam has taken the “angels” that people want to invoke with the believed kemiyah-like powers of the mezuzah, and turned them into the concrete mitzvot that serve as reminders to do God’s will and not to sin. If anything protects a person, Rambam would say, it is not some magical power of the mezuzah, but the psychological/religious impact that it has on a person’s psyche.
Rambam thus has reworked the idea of “angels” and the protection-powers of the mezuzah. But he was not the first to do so. I believe that this approach is already present in the Gemara. For right after the Gemara mentions – in one word! – “that the mezuzah will protect the house” the Gemara continues thusly:
R. Hanina said, Come and see how the character of the Holy One, blessed be He, differs from that [of men] of flesh and blood. When it comes to flesh and blood, the king dwells within, and his servants keep guard on him from without; but with the Holy One, blessed be He, it is not so, for it is His servants that dwell within and He keeps guard over them from without; as it is said, “The Lord is thy keeper; the Lord is thy shade upon thy right hand.” (Ps. 121:6)
What R. Hanina is saying could not be clearer: It is not the mezuzah which protects through some magical powers, but it is God who protects. And it is not the house which is magically protected, but the person who does the mitzvot. The focus on God as the One who affords protection is repeated three times in quick succession: “He keeps guard… The Lord is thy keeper; the Lord is thy shade.” The mezuzah, which is on the right hand of the one who enters the house, does not protect the house. It is rather God who protects the right hand of the one who does the mitzvot.
I believe that this type of reworking is not uncommon in the Gemara. Certainly, there were Jewish religious practices that existed outside the Rabbinic sphere of influence, and archeology and ancient texts attest to the extensive use of and belief in magical amulets at the time of Chazal. It only stands to reason that the amulet function of mezuzot that Rambam so derides was already an extensive phenomenon at the time of Chazal. So how did Chazal deal with this? Our Gemara is the answer – first and foremost, by ignoring it. Chazal deal with mezuzah through a halakhic lens, not through a magical/metaphysical lens. The best way to rob superstitions of their power is to ignore them. The other way that Chazal neutralized this approach was by subtly reworking it. In one word they allude to this power – “so that it protects the house,” and then immediately (re-)frame this as God’s protection of the people (who keep the mitzvah).
In a similar way, I believe, Chazal dealt with popular, non-halakhic taboo and superstitious attitudes around niddah. First, they ignored them, and looked at niddah only through a halakhic lens. And then, in one or two subtle passages, they allude to these attitudes and neutralize and rework them.