Four hundred and fifty years ago, and twelve days and an odd number of hours (depending on the time in which the service was held), in Geneva, Switzerland, John Calvin preached on Deuteronomy 28.15-24. At the beginning of the sermon he explained why God not only encouraged with promised blessings, but warned with threats. This is what he said (according to his English translator):

We have seen the past several days how God entreats His people with promises. Now on the opposite side, He adds threats. And that is not without a good reason, for we see how slow we are when it comes to submitting ourselves to obeying God. Our feet are swift enough to run to evil, as the prophet Isaiah says (59:7), and as it is spoken of in the Proverbs (1:16; Rem. 3:15), but God cannot make us set forth one step to behave ourselves properly, and therefore we must be compelled to it by force. Nevertheless, God certainly begins with gentleness and goodness. And that is why He first sets forth His blessings to those that serve Him. He might very well have begun with threats, but He did not. In so doing He makes a test to see whether we are apt to be taught, by showing Himself fatherly towards us, and by making it to be seen that he seeks nothing other than our benefit, welfare, prosperity, and quietness.

His modern editor footnotes a statement in this quotation. He writes:

Did Calvin really say, “God cannot make us set forth one step to behave ourselves”? Maybe; at least his translator did. If so, this shows that Calvin was not such a stickler for precise language that he refused to use common jargon to get across his ideas. Everybody knew that Calvin believed in irresistible grace. Secondly, Calvin is speaking of God’s “inability” in a covenantal sense, not in a decretal sense. God is unable to get through man’s sinfulness by means of covenantal promises and threats; obviously, God is fully able to change men by means of regenerating grace. Calvin is not so focussed upon decretal theology that he is unable to speak freely about the covenant.