In a novel exposition of this pasuk, Horav Eli Munk, z.l., cites the Zohar Ha’Kadosh who lists four mitzvos by which other nations can “identify” the Jewish People. They are: the Tefillin, which are worn on the head; Shabbos, which is an island in time that distinguishes us from the nations of the world; the Yamim Tovim, which basically have the same distinction as Shabbos and distinguishes us even from those nations who observe a “day of rest”; and the mitzvah of Milah, a permanent sign on our body. In the Talmud, Menachos 55b, however, Chazal only mention the sign of Tefillin Shel Rosh, when citing this pasuk. This sign is seen and acknowledged by all people, as the letter “shin” is engraved upon the Tefillin Shel Rosh. This symbol represents the Shechinah’s presence over us as implied by this pasuk.
Horav Munk observes that the “shin” actually appears twice on the Tefillin Shel Rosh, once with three branches and once with four. He explains that the disparity between the two shins is attributed to their distinct symbolism. The three-branched shin appears on the right side of the Tefillin to symbolize the Shechinah which rests upon the merits of the three Avos, Avraham, Yitzchak and Yaakov. On the left side, the shin has four branches, which allude to the Shechinah’s dominion over the four corners of the earth.
According to the Baalei Kabbalah, the shin with the three branches signifies the world with its failings and restrictions. Consequently, this shin is the one used in the twenty-two letters of the Hebrew alphabet, representing the language of humans. The four-branched shin is part of the Divine alphabet, consisting of twenty-three letters, which is the basis of the Torah. It remains invisible to us to this very day due to our human shortcomings. When Hashem’s kingdom will be restored to its original state, with the advent of Moshiach, we will be privy to the alphabet of the Eternal.