This morning, I read an article about how a Chabad rabbi wants to have a mezuzah affixed on the doorpost of every Jewish home in the state of Montana. If a rabbi wants to bring people closer to Judaism through a certain mitzvah, I'm all for it. I took issue with the rabbi's reasoning behind it: "Montana should be the most protected state in the union. Not only because of our weapons but because of our mezuzahs. We'll be protected by the Second Amendment and by the mezuzahs." I was unaware that a mezuzah can protect a home just as well as an AK-47, or even a home security system for that matter. If one is to treat the mezuzah as an amulet to protect the home from harm, I have a problem with that idea because that line of thinking comes off as superstitious, if not downright idolatrous.
The issue I have here is not whether the mitzvah should be performed. Of course it should be! It's mentioned twice in Deuteronomy (6:9, 11:20). What is going on is yet another polemic debate between rationalists and mystics. From the mystical standpoint, the function of the mezuzah is to act as a metaphysical home security device. Even before continuing on, you should be able to infer my opinion on the matter simply from my self-declaration as a rationalist Jew, especially since I think the superstition surrounding other practices (e.g., kapparot, tashlich) is utter nonsense.
I have already developed a view that G-d is an impersonal G-d and have done so for enough reasons, most notably that of free will. Even if we are to assume that G-d has [extensive] interaction with the world to the point where a mezuzah would have protective qualities, this brings up a plethora of questions. If we are to give credence to the the "power of mezuzah" argument, wouldn't this create a vain focus on one's material possessions, rather than focus on G-d? Because in Mishneh Torah (Hilchot, Mezuzot 5:4), Maimonides considered those who use the mezuzah as an amulet to be fools who have failed to fulfill the mitzvah. And wouldn't affixing a mezuzah for protection be an attempt to circumvent G-d's will? Also, if we are to give this much credence to the power of the mezuzah, couldn't this mentality lead to worshiping the mezuzah itself rather than G-d? (Side note: Maimonides brought up the concern of using talismans and amulets as a form of idolatry in Guide for the Perplexed [III, xxix]) If the mezuzah is supposed to have this level of protection, why even bother with the other 612 mitzvot? Additionally, why is it that G-d, who loves both Jews and non-Jews, would not provide or offer a similar home security device for non-Jews? Why is it that in Israel, a predominantly Jewish country in which 98% of Israeli Jews have mezuzahs affixed to their doorposts, is there still theft and other property-related crime? Are we to believe that in the entire history of the Jewish people, there has never been a Jewish home with an affixed mezuzah that has unfortunately been flooded, burnt, or even in need of some sort of home repair? If the mezuzah were supposed to protect the house, why is it that someone as reputable as R. Moshe Feinstein, zt"l, permit a Jew to buy insurance for his house? Wouldn't that mean that Torah shows us that we can take preventative actions to avoid bad things to happen to us or our property? And that doesn't even take into consideration such events as pogroms, expulsions, the Holocaust, or terrorist attacks in modern-day Israel. Why didn't mezuzahs protect Jews from those atrocities? The point I am trying to convey here is that if we are to take the assertion of "the mezuzah has protective powers" to its logical conclusion, we would be able to consistently observe that power throughout Jewish history. However, that is not the case.
Before continuing, in the event that this line of questioning has not been convincing, I would like to direct you to a stellar piece written by Rabbi Dr. Martin Gordon, former professor at Yeshiva University, in which he refutes the idea that the mezuzah is supposed to act as a protector of Jewish homes.
If the mezuzah is not apotropaic in nature, then what is the purpose of the mezuzah? The mezuzah is a symbol of a Jewish home, much like any ritual item is a symbol of the particularistic aspect of Judaism. The mezuzah can be a reminder of one's need for self-restraint. In my humble opinion, the best place to look would be where the mitzvah is mentioned. The first mentioning is within the first paragraph of Shema (Deuteronomy 6:4-9). There are enough themes in this passage, but one that stands out is the centrality of G-d in one's life. One recognizes His existence, one is supposed to love Him, and one is supposed to study Torah and transmit it to future generations. After that, the passage states that one posts "these words" (הדברים האלה) [in Deut. 6:6] on one's doorposts, i.e., the mezuzah (ibid, 6:9). As Maimonides points out (Mishneh Torah, Hilchot, Mezuzot 6:13), the mezuzah is supposed to remind us of G-d's Oneness when entering and leaving one's house, and thus arouse a sense of love of G-d. In short, the words printed on the mezuzah are not a form of protection from physical harm. Rather, they are a reminder of the importance of G-d in a Jew's life and how that knowledge [of G-d] leads to performing as many mitzvahs as humanly possible.