John Calvin Commentary Jeremiah 48:31

"Therefore will I wail for Moab; yea, I will cry out for all Moab: for the men of Kir-heres shall they mourn." — Jeremiah 48:31 (ASV)

Some think the last word is a proper name, though, according to etymology, it means “the city of potsherd.” Therefore, they offer this rendering: “the strong city.” But Isaiah calls it “Kir-hareseth,” קיר-הרשת; he extends the word by adding a syllable to it, but the word, however, is the same. Then he says, I will think of the men of Kir-cheres. The word הגה, ege, properly means to complain, to whisper, or to murmur; and hence some render the words not improperly, “I will mutter to the men of the city of potsherd.”

The Prophet does not relate here what he would do, as I have reminded you before; but so that he might vividly represent the ruin of Moab, he mentions their howling, crying, and complaints. He then says, I will howl, cry aloud, and with a trembling voice complain, like those who are grievously oppressed with evils; at one time they complain, cry aloud, and howl, and at another they mutter inwardly, grumble and murmur. Thus, the Prophet assumes the character of such persons so that he might more fully set forth the extreme calamity of that nation. He afterwards comes to particulars: