Why do you boast of your valleys—your valleys so fruitful, O faithless daughter? You trust in your riches and say, ‘Who can come against me?’
As the minds of men continually vacillate, because they do not sufficiently consider the infinite power of God, the Prophet, that he might remove all obstacles which might have rendered his prophecy doubtful, now declares that the Ammonites gloried in vain in their valleys. Some understand by valleys a fertile land, well watered. But the Prophet, as I think, refers rather to fortified places.
The Ammonites were next, both in kindred and neighbourhood, to the Moabites, and therefore are next set to the bar. Their country joined to that of the two tribes and a half, on the other side Jordan, and was but a bad neighbour; however, being a neighbour, they shall have a share in these circular predictions. 1.
Commenting on Jeremiah 49:1-6
Wherefore gloriest thou in the valleys,.... Of which there were many in the country of Ammon, fruitful and well watered, which were situated by the rivers of Arnon and Jabbok, the borders of this country, and in which was the plain of the vineyards; see Jdg 11:13; and indeed the whole country was a vale.