“…And you shall bind them for a sign upon your hand, and they shall be for a reminder between your eyes…” – Devarim 6:8

וּקְשַׁרְתָּם לְאוֹת עַל יָדֶךָ וְהָיוּ לְטֹטָפֹת בֵּין עֵינֶיךָ – דברים ו,ח

The Torah commands us to wear Tefillin, comprised of the Tefillin shel Yad tied on the arm, and the Tefillin shel Rosh worn on the head. The Torah’s wording indicates that the mitzvah to don the Tefillin shel Yad is observed actively—“you shall bind them…upon your arm,” whereas the mitzvah to wear Tefillin shel Rosh is observed passively—“they shall be” on your head (between your eyes). This also implies that the mitzvah of Tefillin shel Rosh is fulfilled continuously for as long as the Tefillin is on your head, whereas the mitzvah of Tefillin shel Yad requires and is therefore limited to the act of binding.

This distinction reflects the intended effect of the mitzvah of Tefillin on the person wearing the Tefillin. In the words of the Shulchan Aruch (Orach Chaim 25:5), “G-d commanded that one should place the arm Tefillin near the heart, and the head Tefillin over the brain…so that he shall submit to G-d his soul that is in the brain and his heart that is the seat of his desires and thoughts.”

Therein lies the difference between the Tefillin of the arm and of the head. For as explained in Tanya (Chapters 12-17), the average person can choose the ideas that will occupy his mind, but cannot necessarily influence the desires that his heart will lust. We are capable of restraining ourselves from acting on our impulses, but, with the exception of tzadikim, the perfectly righteous, we have limited influence over our hearts themselves. “One’s mind is under his control, and with it he can meditate as he pleases, on any subject.” However, “it is not a “very near thing” to change one’s heart from worldly desires to a sincere love of G-d” (Tanya, Chapter 17), i.e., to constantly feel drawn toward that which is holy and repulsed by anything unholy.

Accordingly, we are commanded to bind the Tefilin shel Yad near our hearts—actively. We might not be capable of influencing our hearts’ desires to be as pure as they should, but we are able and obligated to restrain them if they are not. The Tefilin shel Rosh, however, must “be” upon our heads, because its desired effect should be perpetual and constant. Since we are capable of controlling our conscious thoughts, our minds can indeed “be” consistently devoted to G-d.

—Likutei Sichos, vol. 39, pp. 24-28