Why is a Mezuzah Hung Diagonally?

The Question
Why isn’t the Mezuzah hung straight?
A simple enough question.
But those of you familiar with the intricacies of Rabbinic tradition know that even the simplest of questions can have deeply complex answers… Well,  today’s your lucky day, because the answer to this particular question is actually quite straightforward, and it involves a debate between two Talmudic commentaries with opposing opinions (bet you didn’t see that comin’…).

The Debate
One of the most famous French rabbis of the twelfth century was Rabbi Solomon ben Isaac, also known as Rashi. His grandson, Rabbenu Tam, felt that mezuzot should be affixed horizontally for the sake of tradition, because the scrolls in their leather cases were originally pushed horizontally into the crevices between the stones around the doorways of homes.Rashi argued that mezuzot should be affixed vertically, in such a way that the top pointed toward the Almighty. They eventually compromised, and agreed that a mezuzah should be hung diagonally, with its top inclined toward the inside. Incidentally, the decision, allowing peace to rein in a Jewish home in twelfth century France, is part of the message of the mezuzah.

Now you know the rest of the story…