Shulchan Aruch, Orach Chayim 35 — שולחן ערוך, אורח חיים לה

How many lines are written in each parasha of the tefillin of the arm and of the head.

seif 1 The Mechaber writes that the custom is to write seven lines in each parasha (each of the four Torah passages placed in the tefillin) of the shel yad (the tefillin worn on the arm). Each parasha of the shel rosh (the tefillin worn on the head) has four lines. If the scribe changed the number of lines, the tefillin are not invalid. The Gra traces this last point to a passage in the Gemara (on daf 34b) about the tefillin of the arm and of the head. The Mishnah Berurah, citing the Tur, explains that the custom comes from a tradition that scribes handed down, one to the next.

The Aruch HaShulchan explains why changing the count does not invalidate the tefillin. The Gemara does not mention the count, and its reason was not revealed to us. Even so, he writes, a scribe who does not follow the custom is not praiseworthy, and his work needs to be checked. He offers his own reason for the numbers. The shel yad corresponds to the heart, which is bound up with time and holds both good and evil, and time is made up of the seven days. The shel rosh corresponds to the mind, which is entirely holy, and its four lines correspond to the letters of Hashem's name.

The Mishnah Berurah adds that the ruling applies to both the shel yad and the shel rosh. Sometimes the only parchment available for the shel yad is too short to fit seven lines without very small writing. In that case he holds it is better to change the count. He cites the Mordechai, brought in siman 32, that beautifying a mitzvah (learned from the verse "zeh Keli ve'anvehu") includes writing somewhat large, so the letters do not wear away quickly. He warns that very small writing, common among some scribes in his day, often has defects from the start. It often lacks the tagin (crowns) on the letters shin, ayin, tet, nun, zayin, gimmel and tzadi. The Gemara requires these tagin, and some Rishonim are strict about them even after the fact. He advises a person not to put such parshiyot in his tefillin unless they are checked very carefully and he knows who wrote them. The writers of such parshiyot are often young men who do not know the laws of writing a Torah scroll, tefillin and mezuzot.

The Mishnah Berurah adds that scribes also had a tradition about which word begins each line. He writes that scribes in his day were not particular about this and let each line begin wherever it happened to fall. Citing the Pri Megadim, he writes that a scribe who wishes to be particular should not stretch or squeeze letters much to make the lines begin with the right words, since that does not beautify tefillin. Stretching or squeezing a little is permitted. The Aruch HaShulchan cites the Shulchan Aruch HaRav that scribes are careful about the number of lines but not about the line beginnings. He permits stretching letters slightly to even the ends of the lines, as long as they do not look larger than the other letters and make the writing look spotted. The Aruch HaShulchan writes that the expert scribes of his country neither stretch nor squeeze letters, and they do match the line beginnings. The Aruch HaShulchan gives the reason that everything the early authorities passed down should be kept, since the hidden reasons of wisdom were revealed to them.