Or HaChaim on Deuteronomy 28:15/אור החיים על דברים כ״ח:ט״ו

1 והיה אם לא תשמע, "It will be if you do not hearken, etc." The Torah made it plain here that unless we fulfil all three aspects of Judasim i.e. Torah study, scrupulous observance of the negative commandments, and the carrying out of positive commandments, some or all of the consequences described forthwith will occur. Learning Torah and not observing the negative commandments does not protect us. Observing both negative and positive commandments but neglecting the study of Torah will still result in the curses of the following verses being fulfilled. Non-observance of each of these three groups of Torah laws will attract its own kind of curses. The Torah commences by describing the punishments in store for the Jewish people if they fail to study Torah. .ארור אתה בעיר, "you will be cursed in the city;" this verse until the words ואבדך מהר, "and you will quickly perish" and the end of verse 20 are a row of escalating curses which are retribution for abandoning Torah, i.e. abandoning Torah study. When one abandons study of the Torah it is viewed as if one had abandoned G'd Himself. This is why this paragraph concludes with the words אשר עזבתני, "for you have abandoned Me."