From The Evolution of God, by Robert Wright:
Look to the world that gave us the Hebrew Bible (what Christians call the Old Testament) and the Koran… there we’ll see how consequential God’s mood changes could be – how, indeed, a burst of vengeful intolerance helped give us monotheism itself; we’ll see that the birth of monotheism left us with what you might call a bad God.
But we’ll also see that this this God then had bursts of moral growth – within both Judaism and Islam – and that the proven ingredients of that growth are around today, just when another such burst is needed.
(excerpted in Time)
From Systematic Theology, by Wayne Grudem:
If God could change… then any change would be either for the better or for the worse. But if God changed for the better, then he was not the best possible being when we first trusted him. And how could we be sure that he is the best possible being now?
But if God could change for the worse (in his very being), then what kind of God might he become? Might he become, for instance, a little bit evil rather than wholly good? And if he could become a little bit evil, then how do we know he could not change to become largely evil – or wholly evil?
… The idea that God could change leads to the horrible possibility that thousands of years from now we might come to live forever in a universe dominated by a wholly evil, omnipotent God. It is hard to imagine any thought more terrifying.