Tefillin are worn daily by Jewish men and boys aged 13 and older, except for on Shabbat and Torah holidays (Passover, Shavuot, Rosh Hashanah, Yom Kippur, Sukkot and Shemini Atzeret).

Technically, they can be worn all day, although most men wear them only during morning services. However, tefillin are not worn at night. Why is that?

Night: Biblical or Rabbinic?

All agree that we don’t wear tefillin at night or on Shabbat. However, there is a disagreement in the Talmud as to why that is.

According to one opinion in the Talmud,1 not wearing tefillin at night is based on the verse in Exodus: “And you shall observe this statute in its appointed time, from day to day.”2 Rabbi Yossi Hagelili explains that “this statute" refers to the mitzvah of tefillin. Accordingly, one who wears tefillin at night would transgress a biblical injunction.

Rabbi Akiva, however, explains that this verse refers to the Paschal lamb, not tefillin. Thus, he posits that in theory the Torah permits one to wear tefillin at night. Nevertheless, the sages decreed that tefillin not be worn at night, lest one fall asleep in the tefillin, which is forbidden.

The halachah follows Rabbi Akiva, and not wearing tefillin at night is treated as a rabbinic ban.3

Shabbat and Holidays

Even Rabbi Akiva is in agreement that not wearing tefillin on Shabbat is biblical. However, while Rabbi Yossi learns this law from the same verse above (see footnote4), Rabbi Akiva sees it in a different verse.

The verse states: “And [the tefillin] shall be for a sign for you on your arm, and for a remembrance between your eyes, so that G‑d’s law shall be in your mouth; for with a strong arm G‑d brought you out of Egypt.”5

Note that tefillin are referred to as a “sign.”

Now on Shabbat and holidays, we don’t require this extra sign, for the days themselves are signs of the covenant. As the verse states: “You must keep My Sabbaths,6 for this is a sign between Me and you throughout the ages.”7

Since we have the sign of the day, the additional sign of tefillin is not required.

Thus, according to the Code of Jewish Law, if one puts on tefillin with the intent of fulfilling the mitzvah on Shabbat or on a holiday, he both transgresses the prohibition of adding to the Torah’s commandments and is considered to have disparaged and demeaned the sign provided by the Shabbat.8

(To understand why these signs, as well as other mitzvot, are not required for women, please see Why Are Women Exempt From Some Mitzvot.)

Two Signs

Many commentaries9 point out that the Torah refers to three mitzvahs as “signs”: brit milah (circumcision),10 Shabbat and tefillin. Thus, they ask, if we are exempt from tefillin on Shabbat because we have the sign of Shabbat, then during the week, too, when we have the sign of circumcision, why the need for the sign of tefillin?

The commentaries explain that in Jewish law, we generally need two witnesses for testimony to be valid. Thus, we actually need two signs that testify to the covenant between us and G‑d. During the week, we have tefillin and circumcision as the signs, and on Shabbat we have Shabbat and circumcision. Having a third sign on Shabbat is unnecessary and undesirable, since it would indicate that the existing witnesses are for some reason insufficient.

Others,11 however, explain that what is needed is not just any sign or covenant between us and G‑d, but one that is specifically associated with G‑d’s taking us out of Egypt. Thus, in this context, only tefillin and Shabbat would be considered signs,12 since brit milah is not specifically associated with the Exodus (or, as others put it,13 other descendants of Abraham were also commanded to circumcise themselves).

Whether on Shabbat or a weekday, these visible signs of our connection to G‑d are of great significance. Our sages tell us that when we are meticulous about these unique mitzvahs, they serve as a powerful deterrent to any negative energies, causing the Divine Presence to rest upon us. We then merit a special portion in the World to Come.14