This is done to accommodate the variant opinions of Rashi (1040–1105) and of his grandson, Rabbeinu Tam, as to whether it should be placed vertically (Rashi) or horizontally (Rabbeinu Tam), and also to imply that God and the Torah (which the mezuzah symbolizes) are entering the room.
Which direction do you hang a mezuzah?
https://www.youtube.com/watch?v=qB1mFgzzUeM
Why put a mezuzah on the door?
In mainstream Rabbinic Judaism, a mezuzah is affixed to the doorpost of Jewish homes to fulfill the mitzvah (Biblical commandment) to "write the words of God on the gates and doorposts of your house" (Deuteronomy 6:9).
Is a mezuzah good luck?
It is customary for religious Jews to touch the mezuzah every time they pass through a door and kiss the fingers that touched it. However, kissing the mezuzah has also become customary for many secular Jews who think of the mezuzah as a good luck charm.
What is the prayer inside a mezuzah?
The mezuzah opens up and inside is the Shema prayer, written on a small piece of parchment. The Shema is the most important prayer in Judaism because it reminds Jewish people that there is only one God.
What does the mezuzah symbolize?
The mezuzah is a piece of parchment scroll with the Shema prayer inscribed on it which is kept in a small case. The purpose of the mezuzah is to act as a constant reminder of God's presence. Jews will often touch the mezuzah as they go through the door. The instruction for this comes from the Torah.