Or HaChaim on Deuteronomy 29:11/אור החיים על דברים כ״ט:י״א

1 לעברך בברית…ובאלתו, "for you to enter (pass) into the covenant…and His curse" (if need be). The reason Moses added the word ובאלתו, "and His curse," will become clearer when we have explained the need for the covenant. Why was the Torah not satisfied with all the admonitions and curses which have already been recorded in the Torah? Some clever people who want to escape the cumulative curses and punishments recorded in chapter 28 may decide to commit a single transgression, such as violating the Sabbath or the laws of idolatry and to thereby become guilty of only a single one of all these penalties seeing that those laws are considered the cornerstones of Judaism. Such people prefer this to first accepting the authority of G'd and the Torah which would make them potentially liable to as many as 36 penalties of Karet. Moses acted astutely when he persuaded these people to accept upon themselves the covenant so that in the future they would be liable for each transgression separately. The oath (curse) would apply if any of these people deliberately flouted the laws he had undertaken to observe as a result of embracing this covenant. Once they had done this, even the intention of violating a fundamental law of Judaism would not safegaurd them against becoming culpable for each transgression separately.