Charles Ellicott Commentary Jeremiah 23:20

"The anger of Jehovah shall not return, until he have executed, and till he have performed the intents of his heart: in the latter days ye shall understand it perfectly." — Jeremiah 23:20 (ASV)

Shall not return ... —that is, will not turn back from its purpose. People should look back on it in the "latter days"—literally, the end of the days (Genesis 49:1; Numbers 24:14; Deuteronomy 4:30; Deuteronomy 31:29), that is, in the then distant future of the exile and the return—and should see that it had done its work of both chastisement and discipline. (Compare Ezekiel 14:22-23.)