This is a redated post.
This is in response to some comments of Ed's.
Most theistic ethics is far beyond the "Becuase I said so" or even the "Because is said so and if you don't you're going to hell." That's an awfully crude and misleading picture of Christian ethics. The overall view that could be sketched goes something like this. God creates humans so that they will be able to get along for an eternity if they develop certain states of character. Certain states of character are reinforced by certain types of actions, and undermined by certain other types of actions. God then reveals to humans (slowly, over a period of evolving understanding) what kinds of actions will result in eternal flourishing. God creates you in such a way that your intended purpose and your inherent purpose are the same. You can only by happy forever by allowing yourself to be converted in to a person with a certain type of character.
It seems to me that, depending on some contingent features of human life, you might be able to be happier overall, by being a completely immoral, selfish SOB if it were really 70 years and out. With an eternity I think that's ruled out.