John Calvin Commentary Leviticus 26:14

"But if ye will not hearken unto me, and will not do all these commandments;" — Leviticus 26:14 (ASV)

But if you will not listen to me. So far, a kind invitation has been set before the people in the form of promises, so that observing the Law might be made pleasant and agreeable. For, as we have already seen, our obedience is only approved by God when we obey willingly. However, since the sluggishness of our flesh needs spurring, threats are also added to inspire terror and, in any case, to compel what should have been performed willingly.

It might seem, then, that threats are absurdly misplaced when used to produce obedience to the Law, which should be voluntary. For the one who is compelled by fear will never love God, and this is the main point of the Law.

But what I have already shown will, in some measure, help to solve this difficulty: namely, that the Law is deadly to transgressors because it holds them firmly under that condemnation from which they would wish to be freed by vain presumptions. At the same time, threats are also useful to the children of God for a different purpose: both to prepare them to fear God sincerely before they are regenerate, and also, after their regeneration, so that their corrupt desires may be daily subdued. For although they sincerely desire to devote themselves entirely to God, they still have to contend continually with the remnants of their flesh.

Therefore, although the primary purpose of threats is to alarm the reprobate, they also apply to believers to stimulate them in their sluggishness, since they are not yet completely regenerate but are still burdened with the remnants of sin.