A mezuzah must be written by a qualified Sofer with special black ink and in quadrilateral (Ashuri) script, the same used to write Torah scrolls.
Many sofrim (scribes) write the mezuzah (as they do the Torah scroll and tefillin) with a reed. The Sages of the Talmud explained that the reed reminds us to be always
A mezuzah has to be written lishmah, for its own sake (i.e., expressly for the sake of the holiness of the mezuzah). Just before writing, the Sofer makes a declaration that he is doing it for the sake of the holiness of the mezuzah. Similar declarations are made before inscribing each Name of G‑d. G‑d-fearing sofrim, especially in Chassidic communities, have a custom to immerse in the mikvah (ritual bath) before writing a mezuzah, and some before writing each Name of G‑d. This is done to remove spiritual uncleanness and to write the mezuzah in purity and holiness. The sofer’s erudition in the pertinent laws is decisive in producing kosher mezuzoth. Nonetheless, his character, behavior, thoughts, in general and while writing the mezuzah in particular, affect the spiritual quality of the mezuzah and its protective power. Therefore, it is highly advisable to purchase mezuzoth from known sofrim with excellent reputations, or from a rabbi who knows a reputable sofer personally and can vouch for him.
For a mezuzah to be kosher, every one of its 713 letters must be written correctly and with white space surrounding it on all four sides. Letters touching each other invalidate the mezuzah. It is explained in the Kabbalah that the white space surrounding the letters in the scroll of Torah or mezuzah has even higher significance than the text itself. As one sofer put it: “We do not write letters; we create spaces.”
A mezuzah must be written exactly in the order the text appears in the Torah. Since it is impossible to check once a mezuzah is ready, one must rely totally on the Sofer in this regard. This emphasizes how important it is to get mezuzoth from a Sofer with a reliable reputation.
The concluding words, “above the earth,” must begin the last line; they should not be written at the end of the line. The Taz explains the reason for this rule as follows:
The preceding line in the mezuzah thus concludes with the word heavens: as the days of the heavens above the earth. By placing the words above the earth at the beginning of the next line, the words heavens and earth are separated from each other as much as possible. This arrangement intimates that “your days may be multiplied; and the days of your children…” (Deuteronomy XI, 21) to an extent equal in magnitude to the distance between the heavens and earth.
The text of a mezuzah must be absolutely identical to the one in the Torah. One word or even one letter missing, misspelled or written incorrectly renders a mezuzah non-kosher. Mass inspections of mezuzoth in the United States and Canada according to Vaad Mishmeres StaM (a highly respected licensing and regulatory agency for sofrim) revealed that 90% of mezuzoth are not kosher. After purchasing a mezuzah, it is highly advisable to have it checked by a qualified sofer. It is often very difficult for a human eye to notice a missed word or letter in a very familiar text. Computers, therefore, come in very handy. Special optical character recognition (OCR) software allows us to recognize handwritten text and to check it by computer. Indeed, many Torah scrolls, tefillin and mezuzoth are checked today on computer. The minimal cost of such inspection makes it very worthwhile.
When the letters in the mezuzah are written properly, some of them have tagin, special crowns or “tittles” (grace lines above the letter which look like a small letter Zayin). Said Rava,
“Seven letters (Gimel, Zayin, Teth, Nun, Ayin, Tzadik, and Shin as well as final Nun and Tzadik) in the mezuzah require three strokes each.”
These crowns have deep mystical significance. Their importance is underscored by the Talmudic narrative relating that Moses, when he ascended to Heaven, found G‑d engaged in affixing these crowns to the letters of the Torah. We find that the ancient tradition regarding tagin was transmitted from generation to generation: Joshua, who according to tradition authored Sefer HaTagin, first engraved the crowns on the twelve stones which he set upon crossing Jordan River.
“Menachem transmitted it to Rabbi Nechunia ben HaKanah, Rabbi Nechunia ben HaKanah transmitted it to Rabbi Elazar ben Arakh, Rabbi Elazar ben Arakh transmitted it to Rabbi Yehoshua, Rabbi Yehoshua transmitted it to Rabbi Akivah.”
It is hard to overestimate the importance of a kosher mezuzah scroll. This is not the place to economize. It is much better to buy the highest quality mezuzoth available and save later on doctor bills and medications! It is also difficult to understand the logic of those who do not hesitate to spend money on expensive mezuzah cases but skimp on the mezuzoth themselves, buying mezuzoth of doubtful validity. The beautiful art of the mezuzah cases notwithstanding, let us remember: it is the mezuzah and not the case that is the mitzvah and which brings the blessings and Divine protection. Thus, it is said,
“A person should not regard lightly the commandment to affix a mezuzah, nor should he be negligent about fulfilling this precept even at great monetary expense.”
It is praiseworthy to beautify a mitzvah, i.e., to perform it in the optimal, most beautiful way. The more beautiful the calligraphy of the text of a mezuzah, the more expensive it most probably will be (and the stronger its protective qualities). It takes 2.5 – 3.5 hours of highly concentrated work for an experienced Sofer to write a good mezuzah. The retail prices on mezuzoth have always been kept to a bare minimum. We find cryptically in the Talmud,
“Said Rabbi Joshua ben Levi: ‘The Men of the Great Assembly observed twenty-four fasts so that those who write [Torah] Scrolls, tefillin and mezuzoth should not become wealthy, for if they became wealthy they would not write.’”