The rule of אין מעבירין על המצוות (“One may not pass by a mitzvah”) establishes that one may not pass over one mitzvah in order to perform another mitzvah. For this reason, Halachah requires that if one keeps his tallit and tefillin in the same bag, he must place the tallit in the front, so that he first encounters the tallit before the tefillin. Otherwise, he will be forced to pass over the tefillin to take the tallit (since the tallit is worn before the tefillin), in violation of the rule of אין מעבירין על המצוות

1) This rule applies only if one intends to presently perform both mitzvot. If one does not intend to perform the mitzvot at this time, then he is certainly permitted to reach over one to take the other. Hence, if the tallit was mistakenly placed behind the tefillin, and one does not intend to use them at this moment, he may remove and rearrange them.[8]

2) If one mistakenly placed the tefillin in front of the tallit and now wishes to wear both the tallit and the tefillin, then some authorities rule that he should first don the tefillin, rather than reaching over the tefillin to take the tallit,[9]whereas others maintain that the tallit should be worn first, even in such a case.[10] To satisfy both opinions, one should rearrange the tallit and tefillin properly, divert his attention from them for a few moments, and then put on the tallit followed by the tefillin.[11]

3) If the tallit which one wears on Shabbat is situated in front of the tallit worn on weekdays, he may reach over the Shabbat tallit to take the weekday tallit.[12]