Siman 35

According to the tradition from the ancients, it is customary to write seven lines in each and every parashah in the shel yad, and four lines in the shel rosh. And if one deviated—he has not disqualified it, since this is not explained in the Gemara. Furthermore, the reason for the matter has not been revealed to us; therefore, it is not a requirement. Nevertheless, a scribe who does not do so is not praiseworthy, and one must investigate him. (And in my humble opinion, the reason appears to be: that the shel yad corresponds to the heart, and the heart is subject to time and contains within it good and evil, and time is comprised of seven days. And the shel rosh corresponds to the brain, which is entirely holy in the Name, and thus there are four lines corresponding to the letters of the Name. And as a support for this, see Zohar Pinhas page 257 side a: "The sixth commandment...", see there. Examine it closely and you will find it simple.)

And these are the words for the beginnings of the lines of the hand-tefillin: 1) "Vayidaber", 2) "et hayom", 3) "yotzim", 4) "latet", 5) "chag", 6) "hahu", 7) "Torat". Second parasha: 1) "Vehayah", 2) "rechem", 3) "besheh", 4) "lemor", 5) "hikshah", 6) "behemah", 7) "le'ot". Third parasha: 1) "Shema", 2) "et", 3) "vehayu", 4) "levavecha", 5) "uvelachtecha", 6) "yadecha", 7) "mezuzot". Fourth parasha: 1) "Vehayah", 2) "uvechol nafshechem", 3) "ve'achalta", 4) "Hashem bachem", 5) "asher Hashem", 6) "bein eineichem", 7) "beitecha uvish'arecha". And the beginnings of the lines of the head-tefillin: 1) "Vayidaber", 2) "mizeh", 3) "hazot", 4) "zeh". Second: 1) "Vehayah", 2) "vechol peter chamor", 3) "miMitzrayim mibeit", 4) "kol peter rechem hazacharim". Third: 1) "Shema", 2) "nafshecha", 3) "levavecha", 4) "al". Fourth: 1) "Vehayah", 2) "esev", 3) "lo titen", 4) "et beneichem".

There is one who wrote that our scribes are meticulous regarding the number of lines and not regarding the beginnings of the lines, and one should not lengthen or shorten the letters for the sake of the beginnings of the lines. However, one may slightly lengthen the letters in the second line in order to align the ends of the lines. And they only forbade extending them so much that it is visible to the eye that they are larger than their counterparts, making the writing appear spotted, as I wrote in Yoreh Deah siman 273 and 275 (the HaGra"z). And the expert scribes of our lands do not lengthen or shorten the letters. And they align the beginnings of the lines, for certainly we must be careful in everything that the ancients commanded us, and to them the mysteries of wisdom were revealed.