With great pleasure, we will now suggest a rationale for housing the four passages we place in the tefillin shel rosh in four separate compartments. This is in contrast to the tefillin shel yad where we place them all in a single compartment. Now, since the tefillin shel yad correspond to Torah she’b’chsav, which was given to us by the mouth of HKB”H, Who is One, Only, and Unequaled, all four passages are place in one chamber.
Tefillin shel rosh, on the other hand, corresponds to Torah she’b’al peh, which encompasses four methods of exegesis represented by the acronym פרד"ס, which stands for פ'שט ר'מז ד'רוש ס'וד: “pshat”—the simple, straightforward understanding of the text; “remez”—the interpretation of the text based on allusions; “drush”—understanding based on more intricate elucidations; “sod”—mystical interpretations of the text based on concealed meanings. Therefore, we were instructed to house the four passages we place in the shel rosh in four separate compartments. This signifies that a Jew must strive to use the intellect in his brain to attain and comprehend all of the various explanations of Torah she’b’al peh employed to interpret Torah she’b’chsav via the methodologies of פרד"ס. For, each of the four methods is unique in its own way.
This is also the rationale for the order of donning the two types of tefillin as explained in the Gemara (Menachos 36a): "כשהוא מניח, מניח של יד ואחר כך מניח של ראש, דכתיב וקשרתם לאות על ידך והדר והיו לטוטפות בין עיניך". When he puts them on, he puts on the “shel yad” first and then puts on the “shel rosh”; for, it is written (ibid. 6, 8): “And bind them as a sign upon your arm,” and subsequently: “and let them be totafos (tefillin) between your eyes.” This mirrors the order in which HKB”H gave us the Torah. He revealed Torah she’b’chsav to us first and subsequently revealed Torah she’b’al peh to us via the Torah scholars in every, single generation. In parallel fashion, we don the tefillin shel yad first, since it corresponds to Torah she’b’chsav; and only afterwards do we don the shel rosh, which corresponds to Torah she’b’al peh.
