The Mezuzah signifies the sanctity and blessing of the Jewish home. Actually it is a portion of the Holy Torah, inscribed in the same manner and script as a Torah. It is an "original" sanctified document in accord with laws and precepts that dare not be compromised.

On this sacred scroll of parchment are inscribed two passages from the Torah, "Shema Yisroel" and "Vehaya" (Deuteronomy 6:4-9)

It is customary, upon entering or leaving a residence, to touch the Mezuzah. This reverence acknowledges our belief in the "Shema Yisroel," the Jewish declaration of faith, which expresses the unity of G-D, the duty of loving and serving Him with our whole being, and our obligation to observe the mitzvoth in and out of the home.

Because it presents basic principles of our faith, the Mezuzah is our responsibility to visitors as well as to ourselves. When a Mezuzah is not valid, its blessings are nullified. Even if one letter or part of a letter is missing or imperfect, the Mezuzah may not be used. Only a "Kosher" Mezuzah sanctifies and protects the home, as well as fulfills the saying of psalmist, "G-D will guard your going and coming from now and for all time."

That is why when you purchase a Mezuzah for yourself or make it a gift to a relative or friend, you are obligated to assure its validity. Be certain that it is hand written and that you obtain it from a reliable source. (Such as from Judaism.com)