The Mezuzah is a small case in which a small hand written scroll of parchment (called a klaf) is placed. The scroll contains the words of the "Shema Israel" (Deuteronomy 6:4-9) passage, in which God commands Jews to keep His words constantly in thier minds and in their hearts. The scroll also contains another passage (Deuteronomy 11:13). The passages are written in Hebrew, and contain 22 lines of 713 painstakingly written letters.
The meaning of the Hebrew word Mezuzah is simply "a doorpost". The meaning of the words "Shema Israel" is "Hear Israel".
On the back of the scroll, a name of God is written. The scroll is then rolled so that the first letter of the Name (the letter Shin) is visible (or, more commonly, the letter Shin is written on the on the upper exterior of the case).
Every time you pass through a door with a Mezuzah on it, you kiss your fingers and touch them to the Mezuzah, expressing love and respect for God and his commandments.
The Mezuzah is not, as some may think, a good-luck charm, nor does it have any connection with the lamb's blood placed on the doorposts in Egypt. Rather, it is a constant reminder of God's presence and God's commandments.
The Mezuzah should be placed on the doorposts of of every Jewish home. Mezuzot should also be placed in every room within the home. A place serving regularly for unclean use, such as a bathroom, is exempt from Mezuzah. The Mezuzah should also be affixed on gates leading to communal places, synagogues, schools, and Jewish ownen business establishments, even on gates of cities, symbolizing the sovereignty of the commandments over the Jewish social and communal life in all its aspects.
The exact placement of a Mezuzah is on the right side of the doorpost (when entering the home or room), on the lower part of the upper third of the doorpost (or around shoulder height for high doorways). The case should be permanently affixed with nails, screws, glue, or strong double-sided tape.
The Mezuzah is affixed at an angle becasue the rabbis could not decide whether it should be placed horizontally or vertically, so they compromised. The top of the Mezuzah should be slanted toward the room the door opens into.
It is proper to remove a Mezuzah when you move, and in fact, it is usually recommended. If you leave it in place, the subsequent owner may treat it with disrespect.
For the Mezuzah to be Kosher, it must meet the following criteria:
The Bibical source of the mitzvah of mezuzah is found twice in Deuteronomy (Devarim), chapter 6, in the paragraph of Shema Yisroel (4-9) and Chapter 9, in the paragragh of Vehaya Im Shamoa (13-21). The Torah states in both paragraphs:
Hear, O Israel, the Lord is our God, the Lord is one. You shall love the Lord, your God, with all your heart, with all your soul, and with all your resources. And these things that I command you today shall be upon your heart. And you shall teach them to your children, and you shall speak of them when you sit in your house and when you go on the way, when you lie down and when you rise up. And you shall bind them as a sign upon your arm and they shall be an ornament between your eyes. And you shall write them upon the doorposts of your house and on your gates.
And it will be that if you hearken to my commandments that I command you today, to love the Lord, your God, and to serve him with all your hearts and all your souls. And I will place rain for your land in its proper time, the early and the late rains, that you may gather in your grain, your wine, and your oil. And I will provide grass in your field for your cattle, and you will eat and you will be satisfied. Watch yourselves, lest your heart be seduced and you turn astray and serve other gods, and prostrate yourselves to them. And the wrath of God will be upon you, and he will restrain the heaven and there will be no rain, and the ground will not yield its produce, and you will be lost quickly from upon the good land that God gives you. And you shall place these words of mine on your hearts and on your souls, and you shall bind them as a sign upon your arms and they shall be ornaments between your eyes. And you shall teach them to your children to discuss them, when you sit in your house and when you go on the way, and when you lie down and when rise up. And you shall write them upon the doorposts of your house and upon your gates, in order to prolong your days and the days of your children upon the good land that God swore to your fathers to give them, like the days of Heaven over earth.