This is almost a truism, but if God is the ultimate source of Good, then God is not Good.
Moreover, if God is the ultimate source of normative behavior (i.e. if the ultimate standard of what should and should not be done is God himself) and God punishes people for not adhering to those norms, this reduces him to a cosmic, omnipotent petulant child.
Omnibenevolence is irrelevant as a characteristic if the person exhibiting it gets to decide what is benevolent with no external standard. If God gets to decide what is good and what is evil, then “good” is reducible to “God’s arbitrary whim.” If God can arbitrarily dictate morality, then there is no way to describe God’s own actions in moral terms.
Which means his wrath at you for sinning is not because you’ve actually done anything wrong. He’s just mad because you didn’t do what he said. And his wrath because of your disobedience can’t be meaningfully described as “just” or “right” in any way if God gets to arbitrarily dictate what “justice” and “right” mean.
In the end, if you worship that kind of God, you’re not worshipping him because he is Good, no matter how you try to spin it. You are worshipping him merely because he is Powerful. He’s just a bully. And you worship him because you are afraid he will hurt you if you don’t.
And that’s double-silly since he might not exist anyway, and even if he does, there’s no particular reason (beyond the impressive philosophical-semantic sleight of hand that theologians have been working at for centuries) to think he’s anything like that.
(Posted as a reaction to this post on Tim’s blog and the ensuing discussion).