In Jeremiah 13:18–27, Jeremiah is told to address the king and queen, telling them of the trouble that will come (using the prophetic past). Unlike many of the preceding chapters, where he tells the Jews to repent of their wrongdoing and change their ways, he here says that they cannot:
הֲיַהֲפֹךְ כּוּשִׁי עוֹרוֹ וְנָמֵר חֲבַרְבֻּרֹתָיו גַּם אַתֶּם תּוּכְלוּ לְהֵיטִיב לִמֻּדֵי הָרֵעַ.
Can the Ethiopian change his skin, or the leopard his spots? Then may ye also do good, that are accustomed to do evil. (JPS)
M'tzudas David explains this as an exaggeration: it would be difficult, but not literally impossible, for the sinners to change their ways. But I'm asking according to view that it would be impossible: Radak explains "the evil won't be able to turn from you, as if it is natural in you"; Mahari Kara says "it is impossible for you that you'll be able to do good".
What purpose did this prophecy serve?
- If the prophecy was true — it would be impossible to repent — then why the prophecy at all? What's the point of telling people they can't repent?
- And if it was false, then (besides the philosophical difficulty in the existence of a false prophecy, which I don't want to get into) how would relaying this (false) prophecy urge the people to repent? Surely if they heard "you can't repent", they wouldn't!