John Calvin Commentary Jeremiah 48:8

"And the destroyer shall come upon every city, and no city shall escape; the valley also shall perish, and the plain shall be destroyed; as Jehovah hath spoken." — Jeremiah 48:8 (ASV)

He confirms the previous verse. Nor should he be considered too wordy. For this prophecy was not announced to sustain the hope and patience of the faithful only for a few days; rather, it was necessary for them to depend for a long time on this promise, which God had given them many years before. This, then, is the reason why the Prophet confirms extensively a truth in itself sufficiently clear.

Come, he says, shall a waster to all the cities. It now appears more clearly why he mentioned some of the cities (though, as we shall see, they were many), so that the Israelites might know that all the land of Moab was to be given up to desolation: Nor shall a city escape, for destroyed shall be the valley and the plain, as Jehovah has spoken.