John Calvin Commentary Jeremiah 12:17

"But if they will not hear, then will I pluck up that nation, plucking up and destroying it, saith Jehovah." — Jeremiah 12:17 (ASV)

As he had shown that there was a sure hope of salvation for his own people if the Gentiles would embrace his mercy, so he now threatens the Gentiles with destruction if they did not repent. For he had promised to be merciful to the Gentiles conditionally, saying, “If they learn the ways of my people, if they submit to my authority”; but now he says, if they will not hear, and so on.

From this we see that God here threatens extreme vengeance to the Gentiles if they did not subject themselves to his yoke and render obedience to him. His object, no doubt, was to terrify the Jews as well as the nations. For if the Gentiles could not despise God with impunity, though he was unknown to them, how inexcusable would the Jews be—who had from their infancy imbibed the true knowledge of the law—if, like the Gentiles, they were perverse and intractable?

In short, we see that God, on one hand, sweetly allured the Jews to render a willing obedience to his law, and, on the other, he threatened them. For as he could by no means bear with the perverseness of the Gentiles, much less could the Jews hope to escape punishment. This is the meaning of the passage. Now another prophecy follows—