The Torah’s command to wear tefillin is fairly cryptic: "And you shall bind them for a sign upon your hand, and they shall be for ornaments between your eyes."1 It is the Oral Tradition that fills in the gaps and describes what tefillin looks like and how to make them. In fact, the Talmud lists ten details about the making of tefillin that are halachah l’Moshe miSinai, traditions given to Moses at Sinai. One of them is that there should be protruding shins formed from the creases in the leather on both the right and left sides of the head tefillin.2

But perhaps more intriguing is that there is a tradition dating back to the early Geonic period (which spanned roughly 589-1000 CE), recorded in the work Shimusha Rabba, that the shin to the right of the wearer should have three heads, and the shin to his left should have four heads.3 The four-headed shin is also mentioned in the Zohar.4

Although the ultimate reasons behind these laws aren’t necessarily knowable, commentaries offer a number of possible explanations for both the regular and the four-headed shin.

Two Types of Letters

Some explain that the two shins correspond to the two ways a letter can be formed: written or engraved. Moses wrote the Torah in a scroll and also received the 10 Commandments engraved on the two tablets on Mount Sinai.

When the letter shin is written in a Torah scroll, ink is applied to create three heads. When it comes to engraving, however, the letters are essentially made out of air—representing the esoteric dimensions of the Torah. The way to engrave the letter shin is by using a frame of four segments, in effect creating a shin with four heads.5

The Number Seven

The Zohar explains that the three- and four-headed shins together make up the number seven. This corresponds to the seven branches of the Menorah in the Holy Temple, which in turn correspond to the seven blessings of the Shema (three blessings in the morning Shema and four blessings in the evening Shema).6

The mitzvah of tefillin is found in the Shema itself, and one is meant to recite the Shema while wearing tefillin.

The Zohar also explains that the tefillin correspond to various other sevens, such as the seven days of the week and the seven sefirot, divine attributes.7 When we put on tefillin, we are connecting our own attributes with divinity and channeling that divine energy into our lives.

Patriarchs and Matriarchs

The three-headed shin corresponds to the three Patriarchs: Abraham, Isaac and Jacob. And the four-headed shin corresponds to the four Matriarchs: Sarah, Rebecca, Rachel and Leah.8

The 613 Mitzvahs of the Torah

Elsewhere, the Zohar explains that tefillin is equal to the entire Torah,9 and all the mitzvahs of the Torah are alluded to in the two shins:10

The letter shin has the numerical value of 300. Thus, two shins make 600.

Putting the two shins together spells the word שש, which means “joy” (reminding us to perform this and all mitzvahs with joy). It also has the numerical value of 6 (if we calculate the value of each letter but truncate all of the zeros, a method known as mispar katan [“small value”]).

Adding the heads of the two shins together equals 7.

Altogether we have 600 + 6 + 7 = 613 mitzvahs!

(This, incidentally, is the source for the custom of looking at the shins of the tefillin when putting on or taking them off, to remind us of all the mitzvahs of the Torah.)

G‑d’s Name

The shin of the head tefillin is part of G‑d’s Name ש-ד-י (Shakkai), which is formed together with the dalet of the knot of the head tefillin straps and the yud-shaped knot of the arm tefillin.11

Expounding on the verse in Deuteronomy “And all the peoples of the earth shall see that G‑d’s Name is proclaimed upon you, and they shall fear you,”12 the Talmud13 explains that this is a reference to the tefillin worn on the head.

Thus, some14 explain that G‑d’s Name is alluded to in the letter shin of the head tefillin itself.

One of the oldest and most common monoalphabetic substitution ciphers used by the mystics (and even found in scriptures15 ) is known as at-bash. In at-bash, the first letter of the alef-bet (alef) is exchanged with the last letter (tav), the second letter (beit) with the penultimate letter (shin), and so on. (The first two pairs of substitutions form the words at-bash.)

If one were to write out G‑d’s name using at-bash,the result would be the letters מ צ פ צ (mem, tzadik, pei, tzadik). All together, these letters equal 300 (40+90+80+90=300), which is the numerical value of the letter shin.

The shin is thus a reflection of G‑d’s name, which strikes terror into the hearts of wrongdoers and protects its wearers. Indeed, when we put on tefillin, this mitzvah brings safety and security to our Jewish brethren, and by extension, peace to the entire world.