“…And you shall inscribe them upon the doorposts of your house and upon your gates…” – Devarim 6:9

וּכְתַבְתָּם עַל מְזֻזוֹת בֵּיתֶךָ וּבִשְׁעָרֶיךָ – דברים ו, ט

Our sages teach that affixing mezuzos to the doorposts of our homes brings security and protection for the house and all its inhabitants (see Talmud, Avodah Zarah 11a). The Zohar (vol. 3, p. 263b) takes this a step further, saying that through the mezuzah “G-d will watch your going out and your coming in, from now and to eternity” (Tehillim 121:8). This means that the mezuzah protects a person not only when he is at home, but even when he is away.

Moreover, since all Jews are connected and accountable for one another, the deeds of one Jew bring merit to all his fellow Jews as well. As such, one Jew’s observance of the mitzvah of mezuzah provides additional safety and security even for others who do not have a mezuzah themselves (though they are obviously not exempt from fulfilling this mitzvah on their own).

The mitzvah of mezuzah and the protection that it provides have particular significance in the Land of Israel, as is evident from the law taught in the Talmud (Menachos 44a): “One who rents a home outside of Israel is exempt from affixing a mezuzah for the first 30 days; from then on, he is obligated. But one who rents a home in the Land of Israel must affix a mezuzah immediately, for the sake of yishuv Eretz Yisrael, settling the Land of Israel.” (Rashi explains that because it is considered improper for a Jew to remove his mezuzah when he leaves his home [Bava Metzia 102a], the renter will not rush to move out and incur the cost of acquiring new mezuzos. Even if he does move out, the home will soon attract another Jewish renter because it is already equipped with a mezuzah.)

This unique law demonstrates that the mitzvah of mezuzah is particularly effective in bringing about yishuv Eretz Yisrael, which, in its truest sense, means not only dwelling there technically, but also living there in comfort and security. (See Vayikra 26:5: “וִישַׁבְתֶּם לָבֶטַח בְּאַרְצְכֶם, you will live securely in your land.”)

This highlights the importance of ensuring that every Jew has a mezuzah on his doorpost. Through this mitzvah, particularly in the Land of Israel, we help create peace and security for ourselves and for the entire Jewish nation.

—Likutei Sichos, vol. 13, pp. 212-216