Halakhah sa Mga Awit 37:37: Ben Ish Hai

Four sections are in the tefillin: Kadesh (Exodus 13:1-10); VeHaya ki Yiviecha (Exodus 13:11-16); Shema (Deuteronomy 6:4-9); and VeHaya im Shemoa (Deuteronomy 11:13-21). And that is the order of their placement according to Rashi, may his memory be blessed. However, according to the understanding of Rabbenu Tam, may his memory be blessed, their order is Kadesh; VeHaya ki Yiviecha; VeHaya im Shemoa; and Shema. But the practice is according to the Rashi's understanding, may his memory be blessed. And the Levush, may his memory be blessed, wrote that once the stand over Ezekiel the prophet's tomb, may his memory be blessed, fell and they found old tefillin there which were [arranged] according to the order of Rashi. So at the beginning, they thought this disagreement was like other disagreements in which one understanding was dispelled. But our teacher, the Ari, may his memory be blessed, came along and said from a tradition spoken by Eliyahu, his memory should be for the good, that both understandings are true and that one should [follow] both of them; and that they would wear two pairs from the days of our teacher, Moshe, up until the Geonim. And so is it found in the Gemara (Eruvin 95b), "there is room on the head to place two pairs." And in the Zohar Chadash it is found that there were some people who would put on two pairs based on the doubt, "as they did not know this secret that both are required." Hence one who fears the Heavens should make two pairs of tefillin, one like the understanding of Rashi and one like the understanding of Rabbenu Tam. And he should grab both of them in his hand and bring them up on his forearm and tie them, one on top of the other. As he needs to put them on together; and not like those who place that of Rashi by itself and that of Rabbenu Tam by itself. It is also necessary that he place the tefillin of Rabbenu Tam above that of Rashi, both with the head and with the arm. For the aspect of Rabbenu Tam's tefillin is greater than the aspect of Rashi's tefillin. Hence the practice is to make the Rabbenu Tam tefillin smaller than that of Rashi. But the connected (hence lower) part of the forearm is the higher. Hence he should first bring up that of Rashi and recite the blessing upon it after he ties it on the biceps; and afterwards bring up that of Rabbenu Tam. And it comes out with this that that of Rabbenu Tam is resting higher than that of Rashi. And all of that is with the boxes; but regarding the straps, he should place the strap of the Rabbenu Tam tefillin below the strap of Rashi. Hence he should make the width of the strap of Rabbenu Tam narrower than that of Rashi, in order that it can be covered by it. And likewise with the head, he should place the Rabbenu Tam tefillin above that of Rashi; and also the knot of the Rabbenu Tam tefillin should be on the nape a little higher than that of Rashi. However one should pass the straps, that hang down from the knot on the nape and below, underneath the Rashi strap, such that it cover it. The hint to this is (Psalms 37:37), "Guard the blameless (tam), and see the upright (yashar, which is Rashi spelled backwards). And there is a reason for all of these things according to [Kabbalah], so one should not change a thing. One should also be careful not to place the box of one over the connection of the other, but rather adjacently, one below the other, with all of them resting upon the flesh - and as I wrote with the help of the Heavens in my holy book, MeKabtziel.