It is written in Sefer a-Hinuh: “The essence of this commandment is to remind a person at any time of faith in the Almighty, Blessed is He, including when entering the house and leaving the house.” The mezuzah reminds the Jew of who he is:
1. Faith in One God.
2. Love for Him and fear of Him.
3. Acceptance of the commandments of the Holy Torah.
Thus, firstly, the mezuzah is a symbol of the Jewish home, which has been attached to the doors of Jewish homes all over the world for thousands of years. Secondly, mezuzah means the unity of the Almighty, who dwells together with the chosen people. She seems to say: “Here lives a Jew who is proud of his Jewishness, believes in God and His Torah, and here dwells a Saint, Blessed is He.” The mezuzah reminds the Jew of being chosen, of responsibility before God and the world. In Shvat 5634 (1974), the Lubavitcher Rebbe said that the mezuzah is active in the world, because thanks to it, the peoples of the world know that it is a Jewish home.