John Calvin Commentary Leviticus 26:15

"and if ye shall reject my statutes, and if your soul abhor mine ordinances, so that ye will not do all my commandments, but break my covenant;" — Leviticus 26:15 (ASV)

And if you shall despise my statutes. This seems only to apply to ungodly and depraved apostates, who deliberately revolt from the service and worship of God. For if a person falls through weakness, and offends from carelessness and inconsideration, he will not be said to have despised God’s Law, or to have made void His covenant.

And certainly, it is probable that God intentionally spoke of blatant rebellion, which could not be excused under the pretext of error. Still, it must be kept in mind that all transgressors, whether they have violated the Law in whole or in part, are brought under the curse.

But God would remind His people in good time how far those eventually go who take the liberty to sin, and also from what source all transgressions arise. For, although everyone who strays from the right path into sin does not altogether reject or detest the Law, yet all sins betray contempt of the Law and tend to break the covenant of God.

He justly, therefore, denounces them as covenant-breakers and proud despisers, unless they obey His commandments. And first, He threatens that He will destroy them with “terror, consumption,” and other diseases; and then He adds external calamities, such as scarcity of grain, violent invasions of enemies, and the plunder of their goods. It will be more fitting to speak of these more fully when explaining the passage in Deuteronomy.