You will find mounted on the doorposts of traditional Jewish homes a small container similar the one pictured on our page. This case or holder is known as a mezuzah (the Hebrew word for "doorpost"). This is not a good-luck charm or an amulet to conjure up protection. Though it should cause us to remember our Exodus from Egypt, it does not have any direct connection with the blood of the Passover lamb which was put on the doorposts while we (Israel) were in Egypt. The Mezuzah is a constant reminder that G-d is always present and that we are to remember the Guide (Torah) for living a good life that He has given to us. Just as we are to wear tzitzit to remind us of all G-d's mitzvot (Commandments), we post Mezuzah to also cause or minds to reflect of His mitzvot.
The commandment to place mezuzot on the doorposts of our houses is derived from Deut. 6:4-9, the passage commonly known as the Shema (Hear, from the first word of the passage). In that passage, HaShem commands us to keep His Words constantly in our minds and in our hearts, by (among other things) writing them on the doorposts of our house. The words of the Shema are written on a very small scroll of parchment, along with the words of a companion passage, Deut. 11:13. On the back of the parchment is written the word 'Sha-dai', along with certain other letters. the parchment is rolled (not folded or creased) from left to right or bottom to top, so that the first word to appear when the Mezuzah is opened is 'Sh-ma'. The scroll is then placed in a protective cover or case and is ready to be put up on the doorpost.
The scroll must be handwritten and must be placed in the case to fulfill the commandment. Gift shops or Book stores usually sell the cases without scrolls or they are sold with mechanically printed scrolls, because a scroll that has been hand written by an "authorized" Sofaer generally costs even more than an elaborately decorated case. According to traditional authorities, mechanically printed scrolls do not fulfill the mitzvah of the mezuzah, nor does an empty case.
As soon as possible after moving into a new home a Mezuzah is nailed or affixed to the right doorpost of the door at an angle (not more than 30 degrees and pointing inward), with a small ceremony called "Channukat Ha-Bayit" (dedication of the house). Family members and close friends are usually invited for something to eat and to offer blessings. Afterward a brief traditional blessing is recited. A great reminder that even though as individuals, we are to have a personal relationship with Avienu Adonai (Father G-d) we are also part of a community and therefore humanly not alone.
Each time one passes through a door with a mezuzah on it, you should touch the mezuzah. This is done to express your love and respect for G-d and His commandments. It is one way for us to be reminded of the commandments contained within the Mezuzah: the Commandments G-d told us to obey for all generations, until heaven and earth pass away.