Or Gedalyahu - 13:16
“והיה לאות על ידכה ולטוטפות בין עיניך, כי בחוזק יד הוציאנו ד' ממצרים” – “And it shall be a sign upon your arm, and an ornament between your eyes, for with a strong hand Hashem took us out of Mitzrayim.” The Kedusha of Tefillin is really different than all other Mitzvos. We know that Tashmishei Mitzvah – items that a Mitzvah was used with, can be thrown out after the Mitzvah is done, for the Kedusha is the actual performance of the Mitzvah, and it is the souls of Yidin who are performing the Mitzvah. Tefillin are not Tashmishei Mitzvah, but rather they are Tashmishei Kedusha, and placing Tefillin on a Yid is showing the ability of the soul of a Yid to completely and truly attach himself to that Kedusha, which ultimately connects the soul with Yetzias Mitzrayim. Tefillin is really supposed to be worn the entire day, and one is not supposed to be מסיח דעת from it – one is to remain focused on the Tefillin he is wearing at all times. We learn this from the Tzitz that the Kohen Gadol wore on his forehead, where he had to wear it all day, and was not to be מסיח דעת. The Tzitz only had one Shem Hashem, and Tefillin has twenty-one Sheimos of Hashem, thus certainly one should not be מסיח דעת when wearing his Tefillin. One is to be connected to the “light” of the Mitzvah, the light that was revealed at Yetzias Mitzrayim, the entire day. Having the proper thoughts in mind while wearing Tefillin truly connects one to Hakodosh Boruch Hu. This is the true image of a Yid, a Yid wearing Tefillin, for that shows that he is completely connected to Hakodosh Boruch Hu, and has complete freedom in matters of Olam Hazeh. This connects him to the freedom of Yetzias Mitzrayim.
