Midrash

Shekhinah is called mezuzah.

Just as all the foods yield to bread1, all nations yield to Jews who have mezuzoth and tefillin.

Commenting on the verse “Happy is the man who hearkeneth to me, watching daily at my gates, waiting outside my doorposts (mezuzoth).” (Proverbs VIII, 34) Rabbi Levi maintained that when one is not sure which way is the entrance to a room (and, therefore, on which side the mezuzah belongs) two mezuzoth should be affixed: one on each side. Rabbi Ishmael maintained that in this case, too, only one mezuzah should be affixed, and the Sages agreed with him.

G‑d is proud of the Jews when they ...affix mezuzoth, don tefillin and tzitzith, perform circumcision...