DEUT1500 It is true that among the tzaddikim there are those who sometimes succumb to sin, as the pasuk says (Koheles 7:20), "For there is no righteous man on earth who does [only] good and does not sin." Yet tzaddikim will subdue their yetzer a hundred times over, and if they fall prey to sin even once, they will not allow it to reoccur, for it leaves them deeply troubled [Yechezkel 6:9], and they repent. Nonetheless, one who is not heedful regarding a known sin, and has not committed to caution concerning it, even if it is one of the more lenient of transgressions, although he may be heedful of all other transgressions within the Torah – – the Sages of Israel have referred to him as (Chulin 4b), "an apostate regarding one matter," who is counted among the evildoers [He is similar to a mumar lehach'is, an apostate who acts out of spite, since he shows no concern for that one prohibition (see Zeh Hasha'ar).], and whose transgression will be too great to bear. For if a servant explicitly tells his master: "I am willing to fulfill whatever you ask of me, with the exclusion of one thing," he has already divested himself of the yoke of servitude to his master [since he arbitrarily chooses which mitzvos to fulfill and which not to, he is referred to as a porek ol -- one who has divested himself of the yoke of servitude to Hashem", and he will do as he sees fit. Regarding this matter the pasuk says [this verse], "Cursed is he who does not uphold the words of this Torah to do them." This means: who is not committed to the fulfillment of all the words of the Torah, from beginning to end. [The expression] "who does not uphold… to do" attests to this--for it does not [simply] say, "who does not do them." [The curse is not directed to any sinner, but only to one who is not committed to full mitzvah observance. See Ramban and Seforno, ad loc.]