(Ibid. 16) "And it shall be as a sign upon your hand, etc.": In four places, the mitzvah of tefillin (leather phylacteries worn during prayer) is mentioned: (Exodus 13:1-10) "Sanctify unto Me every first-born, etc."; (Ibid. 11-16) "And it shall be, when the L-rd brings you, etc."; (Devarim 6:4-9) "Shema, etc."; and (Ibid. 11:13-21) "And it will be if you hearken, etc." From here they ruled: The mitzvah of tefillin: Four sections in the arm-piece on one parchment; four sections in the head-piece on four (distinct) parchments. And these are: "Sanctify unto Me," "And it shall be, when the L-rd brings you," "Shema," "And it will be if you hearken." If they were not written in this order, they must be secreted.