Without question, God is the main character in Isaiah. Not only does he executemost of the wrath and mercy that happens in the course of the book, he also speaks most of the words in the book, too (even though he uses Isaiah to convey his message). The book continually hammers on the idea—hence, God himself continually hammers on the idea—that God is supremely competent. He's directing everything the way he wants it to go.
Isaiah's God is pretty "up and down," to put it one way. One second he's dishing out total destruction and worldwide devastation: women are getting afflicted with horrible diseases for wearing too much jewelry, the infant children of Babylon are getting smashed to pieces by invading Persians. All of this is taking place not just with God's permission, but with God's pre-planned direction.
Still, despite his predilection for massive violence, God will suddenly swing into a more merciful mood. At the end of history, he'll create a world where all violence ends, even between animals—lions eat the same straw that oxen eat. Peace, rather than war, will be God's catchword for eternity.
So, why is this Deity so all over the place? Were the authors of Isaiah simply of different opinions about God, unable to get over their own contradictions? Well, no. It seems like God's wrath is a necessary step in the evolution of humanity, before the time for mercy comes: "Grain is crushed for bread, but one does not thresh it forever; one drives the cart wheel and horses over it, but does not pulverize it. This also comes from the Lord of hosts; he is wonderful in counsel, and excellent in wisdom" (28:27-29). Isaiah's God says that, in the same way that grain needs to be crushed and ground up before it can be turned into flour and baked into bread, all this wrath is just preparing the way for the final Good Time.
We guess you could say it's another way to bake a cake, like in this haunting and deeply disturbing video.
God is passionately involved with Israel, which he variously calls both a daughter and a wife. But, well, they've got issues. Israel is either a disobedient, rebellious child or an adulterous wife. Probably the average person's response to a rebellious child or an adulterous wife is not to send Babylon or Assyria to invade and terrorize them. But that, indeed, is God's response.
All the same, God constantly alternates between fiery condemnation and consolation, threats of violence and promises of mercy. He gives out carrots and he gives out sticks. Sometimes Israel, instead of appearing as a human, appears as a vineyard with God as its gardener. Rather than raging against Israel for its adultery, God rages against it for yielding up bad grapes.
God's "biographer" (although, if you buy the divinely inspired idea, God would be his own autobiographer) Jack Miles sees Isaiah as providing a uniquely interesting and important look at God's personality. Whereas Jeremiah gives a particularly depressed view of God and providence—obsessed with impending destruction and doom—Isaiah is hyped up and speedy. God isn't just totally bent on tearing things up in Isaiah. It's more like a spiritualized frenzy, a passion for breaking it all down in order to set it right. (As for the other major prophet, Ezekiel: rather than giving a hyper or depressed look at God, he gives a trippy, psychedelic view of God, with far-out visions of God's chariot.)
This doesn't mean that Isaiah is the hype-man—the Flava Flav, if you will—of the major prophets. It means that his view of God is one that ultimately highlights God's mercy and goodness. The God of strict justice is very much in play in Isaiah. Still, God's wrath, justice, strictness and the general tendency to "harsh your mellow" are bound to eventually fade into the background when righteousness comes to reign. The message, overall, is one of peace, mercy, and reconciliation.