Rashi on Deuteronomy 27:26/רש"י על דברים כ״ז:כ״ו

1אשר לא יקים [CURSED BE] HE THAT DOES NOT UPHOLD [ALL THE WORDS OF THIS LAW TO DO] — Here (in these words) he included the entire Torah under a curse and they took it upon them pledging themselves by an execration and an oath.