We
find in the Torah three mitzvot that are referred to as a
"sign" or
"covenant" between God and the Jewish people. One is Shabbat, another
is Bris, and the third is tefillin (phylacteries).
The
presence of two of these "signs" is constant: On weekdays the two are the Bris and tefillin; On Shabbat the two signs
are the Bris and Shabbat. (This is one
reason why we do not wear tefillin on Shabbat).
An
allegorical hint to this idea can be found in the Hebrew word Shabbat. Shabbat is spelled Shin, Beit,
Tof. The letters form an acronym for "Shabbat Bimkom tefillin" — Shabbat
in place of tefillin." In
reverse it reads: "Tefillin Bimkom Shabbat." - tefillin
in place of Shabbat."
