— A mezuzah (meh – ZOOZ – zah) is a box or case which we attach to the doorframe of a Jewish home.
— The little box or case contains a piece of parchment called a klaf. (See photo below.)
— The parchment has Deuteronomy 6:4-9 and 11:13-21 written on it by a specially trained scribe, in Hebrew:
Hear, O Israel: The Eternal our God, the Eternal is one. Love the Eternal your God with all your heart and with all your soul and with all your strength. These commandments that I give you today are to be on your hearts. Impress them on your children. Talk about them when you sit at home and when you walk along the road, when you lie down and when you get up. Tie them as symbols on your hands and bind them on your foreheads. Write them on the doorframes of your houses and on your gates.
So if you faithfully obey the commands I am giving you today—to love the Lord your God and to serve him with all your heart and with all your soul— then I will send rain on your land in its season, both autumn and spring rains, so that you may gather in your grain, new wine and olive oil. I will provide grass in the fields for your cattle, and you will eat and be satisfied.
Be careful, or you will be enticed to turn away and worship other gods and bow down to them. Then theLord’s anger will burn against you, and he will shut up the heavens so that it will not rain and the ground will yield no produce, and you will soon perish from the good land the Lord is giving you. Fix these words of mine in your hearts and minds; tie them as symbols on your hands and bind them on your foreheads. Teach them to your children, talking about them when you sit at home and when you walk along the road, when you lie down and when you get up. 20 Write them on the doorframes of your houses and on your gates, so that your days and the days of your children may be many in the land the Lord swore to give your ancestors, as many as the days that the heavens are above the earth.
— By putting the mezuzah up, the Jews who live in this home fulfill the commandment to “write [these words] on the doorposts.”
— The box and the parchment serve as a reminder that a Jewish home is a holy place.
— Some Jewish homes have mezuzot (plural) on all the doorways except the bathroom doors. Others put a mezuzah only on the main entrance.
For more about the mitzvah [commandment] of the mezuzah, read more in this article in the Jewish Virtual Library.