“And you shall bind them [the words that I command you today] for a sign upon your arm, and they shall be for frontlets between your eyes... (Deuteronomy 6:8)”
The above verse refers to the mitzvah of tefillin. (The common translation of tefillin is “phylacteries.”)
Tefillin are small black leather boxes that are strapped to the arm (tefillin shel yad) and to the head (tefillin shel rosh). In order to be kosher: 1) The scrolls with the Torah verses must be written on parchment with ink, bound by the hair of a kosher animal and wrapped in a strip of cloth. 2) The black boxes (made from the hides of kosher animals) and their stitches (sewn with the sinew of a kosher animal) must be perfectly square with an opening made for the straps. The tefillin shel rosh must have the letter shin embossed on both its right and left sides. 3) The straps must be colored black.
The box of the tefillin shel yad (arm) has a single compartment in which is placed a single scroll containing the four Torah passages that refer to this mitzvah: Exodus 13:1-10, Exodus 13:11-16, Deuteronomy 6:4-9 and Deuteronomy 11:13-21. The tefillin shel yad (of the arm) is always placed on the “weaker” arm. Thus righties place them on their left arms and lefties on their right arms. The placement of the tefillin on one’s less dominant hand demonstrates the desire to use one’s entire body to fulfill the commandments. The box of the tefillin shel yad is placed on the inner arm above the elbow, on top of the muscle, and is lined up to aim at one’s heart, the center of one’s emotions and desires. The strap of the tefillin shel yad is wrapped around the lower arm seven times. Finally, the strap is wrapped around one’s hand so that the different criss-crossings create the letters shin, daled and yud, Sha’dai, a name of God representing “He Who sets boundaries on the world.”
The box of the tefillin shel rosh has four separate compartments formed from one piece of leather--each of the four Biblical sections is written on a separate scroll and placed in its own individual compartment. The box of the tefillin shel rosh (of the head) is placed centrally just above the forehead, while the knot that ties the two ends of the strap of the tefillin rests just above the nape of the neck. Just as the tefillin shel yad symbolically represents dedicating one’s emotions to serving God, the tefillin shel rosh represents the dedication of one’s intellect to serving the Almighty.
It should be noted that the way in which the tefillin are worn is profoundly symbolic. The actual method for “laying tefillin,” as it is called, is intricate and should be reviewed with a rabbi or one experienced in putting on tefillin.