Fields in various Moabite hot-spots—like the oh-so-trendy Heshbon and the rather posh locale of Sibmah—are going to see their vines and fields dry up. No one's getting drunk off of those grapes again, even though they used to make the (more kingly version of the) box wines of their day, which were diffused far and wide over the globe.
But this really upsets Isaiah—or God, if God's weeping through Isaiah. He's going to cry for all the wine grapes that have gone to waste in Sibmah.
No one's going to shout joyfully over the fruit and wine harvest, because all those people and plants are going to be dead.
No one's going to be around to tread out the wine or sing happy songs, or do anything nice like that. But Isaiah's heart's going to throb "like a harp" for Moab.
When Moab tries to pray in the sanctuary, it's not going to work.
This, says Isaiah, is what God predicted would happen to Moab. And in three years, this is all going to come to pass. Very few are going to survive. The ones that do will be feeble—bad times, gang.