"All the nations of the earth will realize that G‑d's name is proclaimed over you and they will be afraid of you." (Deut. 28:10)

Rabbi Eliezer ben Hyrkanus in the Talmud (Menachot 35) explains the words: "G‑d's name is proclaimed over you" as a reference to the tefillin on the head. This would account for the fact that that the head tefillin has two letters shin - a three stemmed one and a four-stemmed one - as part of its housing, an official requirement dating back to the times of Moses. It is as if our verse tells us that when the nations of the world observe these two letters on our head tefillin, they will be seized by a sense of awe and develop fear of us.

Another mystical aspect of this verse is that when you read the alphabet in a reverse order i.e. exchanging alef [the first letter] with taf [the last], or beit [the second letter] with shin [next-to-last], you will find that the letters of the great and holy Four-Letter Name of G‑d [Havayah], are now mem-tzadi-peh-tzadi, whose combined numerical value is 300, the same as the letter shin! During the year, there are 300 days on which tefillin are worn (after Shabbats and festival days have been deducted from the 365 days of the solar year).

The straps…indicate that the Divine input into this earth's domain occurs from above….

If you will look still more deeply into the significance of this letter shin, you will find that it is an allusion to the Shechinah, whose first letter is shin, a manifestation of the presence of G‑d. The shin of the four "heads" is an allusion to the Shechinah which orbits [surrounds] the entire globe as well as outer space and which exerts its influence on the four "chayot" [angels] of the divine entourage described both in the visions of Ezekiel and Isaiah.

The strap to which the head tefillin is tied, and which has a knot in the shape of the letter dalet, is an allusion to the four kinds of wind which operate on earth from four directions guided by the Shechinah. These winds sometimes blow upwards and sometimes downwards. The straps (the part under the knot which looks like the letter dalet and which continue in a downward direction) indicate that the Divine input into this earth's domain occurs from above in a downward direction, i.e. emanates from the higher emanations chochma and bina.

[Selected with permission from the seven-volume English edition of "The Torah Commentary of Rebbeinu Bachya" by Eliyahu Munk.]