Isaiah sings a hymn about how his beloved (God) planted a vineyard on a hill and built a watchtower in the middle of it. God thought it would yield nice, domesticated grapes, but it didn't. Instead, it yielded wild grapes (that came in from outside the vineyard).
Now, speaking in God's voice, Isaiah asks what more he could've done to protect the vineyard? The implied answer is "nothing."
So, since the vineyard just yielded up all these lousy wild grapes, God's going to totally destroy it. He'll remove the hedge and won't water it, just let it get wiped out.
Isaiah, revealing the significance of this metaphor, explains that the house of Israel and the people of Judah are themselves the vineyard. Instead of yielding up good grapes (righteousness and justice), they yielded up wild grapes (wickedness and injustice). That's pretty sour.
No Happy Hour
God attacks the greedy people who are taking over all the land, adding field after field into their own ownership.
He says that many houses will be emptied and made desolate, and that all these fields will end up yielding barely anything.
Next, God goes after people who are waking up early and drinking hard booze, then keeping it up through the evening. God says that such people are just pleasure-seekers who ignore his own righteous ways.
He says this is a big part of the reason why the people are hungering, the nobles are starving, and others are getting sent into exile.
Sheol (the underworld) "has enlarged its appetite": everyone's dying. All the nobles of Jerusalem are dying out, and everyone else is being humbled.
Lambs will be able to play in the ruins of the city. (Well, at least the lambs will be happy.)
Hold the Cosmopolitan
God calls out the people who impatiently keep saying that he should hurry up and manifest his divine plan.
He says that they're just sinners who think what's good is evil and what's evil is good. Further calling them out, God condemns such people for thinking that they're so wise, and also for cultivating bar-tending skills at the expense of righteousness (he says they're "heroes at drinking wine and valiant at mixing drink").
He also says that they're corrupt, can be bribed to get guilty people off, and deal unjustly with the innocent.
Whistlin' Dixie (or, uh, Assyria)
All of these people (says God) are going to die like a withering plant or dry grass getting burned up in a fire for refusing to follow God's instructions.
This tends to make God really angry. God's already filled the streets up with corpses and he's still miffed, won't turn his wrath away.
God's going to whistle up a foreign army from far away. They'll have a really high-end, state-of-the-art army—great arrows and chariots and all the rest. Like devouring lions, they'll sweep down and destroy Judah. Darkness and distress will be the order of the day.