Halakha Ulangan 6:6: Mishneh Torah, Tefillin, Mezuzah and the Torah Scroll, Sefer HaMitzvot, Shev Shmateta & Shulchan Arukh, Orach Chayim

Phylacteries and Mezuzoth may only be written in square Hebrew script. Permission was also given to write scrolls of the Law in Greek characters but not in those of any other foreign tongue. The ancient Greek script has gone out of use, been corrupted and become obsolete. Hence, at the present day, all three religious articles,—Scroll of the Law, Tephillin and Mezuzah,—are only written in the square Hebrew script. Care must be taken in writing that no letter shall adhere to any other letter; for any letter which is not completely surrounded on all four sides by a blank space of parchment has been improperly written. Any letter that cannot be read by a child of ordinary intelligence—not particularly bright or dull—is improperly written. Thus a Yod must not be like a Vav nor a Vav like a Yod, nor a Koph like a Beth, nor a Beth like a Koph, nor a Daleth like a Resh, nor a Resh like a Daleth, etc., so that the reader may be able to read fluently.

The 3rd mitzva is that we are commanded to love G‑d (exalted be He), i.e. to meditate upon and closely examine His mitzvos, His commandments, and His works, in order to understand Him; and through this understanding to achieve a feeling of ecstasy. This is the goal of the commandment to love G‑d. [We can see that meditation is the way to create this feeling of love1 from] the Sifri: "From the statement, 'You shall love G‑d your Lord'2, can I know how to love G‑d? The Torah therefore says, 'and these words which I command you today shall be upon your heart'3; i.e. that through this [meditation about His commandments] you will understand the nature of 'the One Who spoke, and thereby brought the world into being.' "From this it is clear that meditation will lead to understanding, and then a feeling of enjoyment and love will follow automatically [since the second verse explains the way to reach the goal of the previous verse.]Our Sages also said that this mitzvah includes calling out to all mankind to serve G‑d (exalted be He) and to believe in Him. This is because when you love a person, for example, you praise him and call out to others to draw close to him. So too, if you truly love G‑d — through your understanding and realization of His true existence — you will certainly spread this true knowledge that you know to the ignorant and the foolish.[We see that this mitzvah includes spreading love for G‑d to others from] the Sifri: " 'You shall love G‑d,' i.e. make Him beloved among the creatures as your father Avraham did, as it is written, 'The souls that he made in Charan.'4"The meaning of this Sifri: Avraham, as a result of his deep understanding of G‑d, acquired love for G‑d, as the verse testifies, "Avraham, who loved Me"5. This powerful love therefore caused him to call out to all mankind to believe in G‑d. So too, you shall love Him to the extent that you draw others to Him.

The phylactery of the hand is bound on the left arm over the biceps muscle which is the flesh that stands out on the upper arm that is intermediate between the shoulder-blade and forearm, so that when the upper arm is held close to the ribs, the phylactery will be opposite the heart and thus the precept will be fulfilled, "And these words … shall be upon thine heart" (Deuteronomy 6:6).