John Calvin on Jeremiah 48:18

Here the Prophet turns to address the city Dibon, which was renowned among that people. The mode of speaking is well known; he calls the people of the city the daughter of Dibon; and he calls the daughter an inhabitant, because the Moabites, as it has been said, ever rested in safety and quietness in their own habitations, for no one disturbed them. It is, then, the same as though he had said, “Ye who have hitherto been in a quiet state, descend now from your glory, and dwell in thirst.” The verb “dwell” favors the idea adopted by some, that צמא means here a dry or thirsty land. - Ed By thirst he means the want of all things. Thirst is set in opposition to glory; but it is more than if the Prophet had mentioned disgrace or poverty; for there are many who are otherwise oppressed by want, and yet find fountains or streams; but when there is no drop of water to quench thirst, it is an extreme misery.

We hence see that the Prophet exaggerates the punishment of the Moabites, when he says that the citizens of Dibon would sit in thirst, because, he says, ascended against thee has the waster, עלה here, as in Jeremiah 48:15, is a participle, and so the verb which follows. The “waster” is represented as then on his way, —

For the waster of Moab is ascending against thee, The destroyer of thy fortresses.

— Ed and the destroyer of thy fortresses. We may hence conclude that the city was on all sides fortified, so that it thought its defences sufficient to keep off enemies. But the Prophet derides this presumption, because the Chaldeans would come to pull down and destroy all these strongholds. It follows —

Jeremiah 48:19

19. O inhabitant of Aroer, stand by the way, and espy; ask him that fleeth, and her that escapeth, and say, What is done?

19. Super viam consiste et speculare habitatrix Aroer; interroga fugientem et eam quae elapsa fuerit, dic, Quid factum est (quid accidit?)