DEUT75 Among those injunctions that depend on [the thoughts of] the heart: "Beware, lest you forget Hashem, your God" (Devarim 8:11). Our Sages, z"l, said (Makos 13b): "Wherever it says, 'beware,' 'lest,' and 'do not,' it is referring to a negative commandment." Herein we have been admonished to remember Hashem at all times. One is obligated to try and constantly internalize those norms of conduct that are bound to [this] remembering [I.e., A person must exert himself to acquire those characteristics that are fully attained only when one recalls Hashem's presence (Zeh Hasha'ar)] --such as fearing Hashem, modesty, refinement of thought, and proper development of character traits. By recalling Hashem's Name, the holy seed [of Yisrael] requires every demeanor of beauty adorning its owner, as the pasuk says (Yeshayahu 45:25), "Through Hashem, all the seed of Yisrael will become righteous and glorified." ... "Beware, and diligently safeguard your soul, lest you forget the things you saw" [this verse]. Our Sages, z"l, said (Menachos 99b) that anyone who forgets one thing from what he has learned has transgressed two prohibitions. [I.e., "Beware" and "lest"; see previous paragraph] you would perhaps think that this also applies to one who has difficulty retaining what he has learned? Therefore the verse tells us (ibid.), "lest they be removed from your heart"-- the pasuk is referring only to one who removes [the words of Torah] from his heart by the neglect of Torah study, and by not constantly delving into it.