“[Mitzvot] are commandments, but the word mitzvah also comes from the root tzavta, which means ‘connection.’ A mitzvah creates a bond between G‑d who commands and man who performs. In a sense, that makes tefillin the ultimate mitzvah. We’re commanded to literally bind ourselves to the one and only G‑d.
More specifically, one of the boxes is placed on the arm so as to rest against the heart, the seat of the emotions, and the leather strap is wound around the left arm and hand. The other box is placed on the head, above the forehead. This teaches us to dedicate ourselves to the service of G‑d in all that we think, feel and do.
When you put on tefillin, you’ll be connecting to the Infinite, fulfilling G‑d’s will, and reminding yourself to be a better person. But you’ll also be doing something that your great-great-grandfather did in exactly the same way. And when you do it, you’re increasing the chances that your great-great-grandchildren will want to do it too. Those straps don’t connect you just to G‑d; they connect you to your past, to your future, to your people.”