Deuteronomy 27:26

The twelve tribes, each and every, shall pronounce the blessings altogether, and the curses altogether. In blessing, they shall turn their faces (in pronouncing) word by word towards Mount Gerezim, and shall say: Blessed is the man who confirmeth the words of this law to perform them. In cursing, they shall turn their faces towards Mount Ebal, and say: Accursed is the man who confirmeth not the words of this law to perform them. And all shall answer together, and say, Amen. These words were spoken at Sinai, and repeated in the tabernacle of ordinance, and (again) the third time on the plains of Moab, in twelve sentences (words), as the word of every tribe; and each several commandment (was thus) ratified by thirty and six adjurations.

Some people claim that the verse who will not fulfill… refers to the entire Torah. Others claim that it only denotes the abovementioned prohibitions; but these people have spoken vacuously, since Scripture proceeds to say and practice them. In my opinion, having already cursed all those who violate the abovementioned negative commandments, Scripture now curses all those who secretly violate the positive commandments. That is why Scripture uses the form and practice them.

CURSED BE HE THAT CONFIRMETH NOT THE WORDS OF THIS LAW. “Here [in these words] he included the entire Torah and they took it upon themselves with an imprecation and an oath [to observe all the commandments thereof].” This is Rashi’s language. In my opinion this “acceptance” requires that one avow the commandments in his heart and consider them as the truth, believe that he who observes them will be requited with the best of rewards and he who transgresses them will be punished, and if someone denies any of them, or considers it annulled forever he will be cursed. However, if one transgressed any commandment, such as eating swine or some abominable thing because of his desire, or he did not make a Booth or take the palm-branch [on the Festival of Tabernacles] because of laziness, he is not included within this ban, for Scripture did not say “who does not perform the words of this Law” but it states that ‘confirmeth’ not the words of this Law to do them, similar to the expression the Jews ordained, and took upon them [and upon their seed … so as it should not fail, that they would keep these two days — of Purim — according to the writing thereof]. Thus the verse [before us] is the ban on those who rebel [against the authority of the Torah] and who deny [its validity].
Now, I have seen the following text in Yerushalmi Sotah: “Asher lo yakim [literally: ‘that does not stand up’ — the words of this Law]. But is there ‘a falling Law?’ Rabbi Shimon ben Yakim says, This refers to the officer [of the Synagogue, as explained further on]. Rabbi Shimon ben Chalafta says, This is the court on earth, because Rav Yehudah and Rav Hunah in the name of Shmuel said: Due to this verse [asher lo yakim (that confirmeth not)] King Josiah rent his clothes, (ibid). The question now arises as to which particular verse affected the king to rend his clothes? Rav Hunah in the name of Shmuel said that it was the verse before us, asher lo yakim — ‘that confirmeth not’ the words of this Law, and since he was king, he felt it his responsibility to re-institute the authority of the Law. saying, ‘The duty is upon me to stand up [the Law].’ Rabbi Asi in the name of Rabbi Tanchum the son of Chiya said, [Even if a person] learned and taught [Torah], observed and fulfilled [its commandments], but had the means to enable [others to study the Torah] and did not do so — he is included within the curse” [mentioned in the …

ארור אשר לא יקים, this is a blanket curse applying to all sins committed in private, the sinner making sure he is not observed.

אשר לא יקים את דברי התורה הזאת לעשות אותם, who neither observes nor admits that they are all worth observing. but, who in his arrogance, considers some commandment or commandment of the Torah not worth his while observing. In the Talmud such a person is considered a “heretic because he rejects a single one of G’d’s commandments.”