NUM202 … the mitzvos of tefillin and of mezuzah … are positive commandments, associated with God's sovereignty [Rabbeinu Yonah on Berachos 15a explains that by wearing tefillin on the head and arm, one subjugates his soul and body to Hashem (Zeh Hasha'ar)], and for this reason they are mentioned in the sections of Shema Yisrael [The reading of Shema is the quintessence of accepting Hashem's sovereignty (See Mishnah Berachos 2:2). Tefillin and mezuzah are mentioned in the first two sections of Kerias Shema (Devarim 6:8, 9 and 11:18, 20)]. In this manner you will be able to reflect upon the punishment of one who neglects these mitzvos, for such a person breaks the yoke [of Heaven] and severs his bonds [Tehillim 2:3]. ... Regarding the mitzvah of tzitzis, our Sages, z"l, said (Sifrei 15:40), that tzitzis add [to one's] holiness, as the pasuk says [this verse], "That you may remember and perform all My Commandments, and be holy unto your God." Although the mitzvah of tzitsis is only incumbent upon one who has a garment of four corners, and one who does not possess such a garment is not required to buy one, nevertheless, our Sages, z"l said (Menachos 41a) that when difficult times come he will surely be punished for not coveting the beauty of this mitzvah and its reward [enough] to forgo the circumstances that leads to its obligation – – acquiring a garment of four corners [in order] to place tzitsis on them.