The religious argument that all morality would be relativistic without god’s law, in addition to being false outright, makes an argument which cannot be fulfilled. Without god’s law, the say, we’d have no idea what was truly good. In other words, knowledge of good and evil in itself is dependent on knowledge of god and the truth of its moral authority.
The usual argument is that god is by definition perfect, and thus its morality is necessarily good. Therefore knowledge of god’s nature – whatever it might be – is knowledge of perfect morality.
Note, however, that this argument presumes to tell god what it must do, which among other things is to tell the truth. But an omnipotent god must retain the ability to lie and therefore no revelation of god can be accepted at face value. In other words, no command of god can be considered either perfect or good of its own nature. This leaves humans once again in the position of deciding for themselves what is good and what is evil.
What’s more, if assume god exists, it doesn’t naturally follow that this god has established absolute morality. Who among the theists can demand of god that it establishes such law?God itself might well have created relativistic morality.
From a theist’s point of view, this moves the problem of knowledge of good and evil from god into untenable territory. The reason is simple, as it is a necessary property of god that its mental capacity is far beyond the comprehension of man. The task of determining what god actually thinks, then, is beyond the possibilities god has given us.
Have we not some interior, a priori knowledge of good and evil? Does this knowledge not confirm for us the truth of god’s morality? Now here are dangerous questions for theists to ask, as any innate moral sense would seem to contradict their argument that without god, man would quickly degenerate into baby eating monsters (I’m not kidding, I’ve had this example put to me several times). So the usual answer to this is to argue that god has provided us this innate sense. Does this not prove the goodness of god’s morality?
It cannot. The inherent unreliability of man’s knowledge of god forces us to find some means of determining for ourselves if god’s word is true. We judge god, in other words – and cannot escape doing so.
In the end theists find themselves in the very position atheists do regarding morality; they must determine it for themselves. In this regard, simply choosing to accept biblical morality is arbitrary, and thus definitely relativistic. The inevitable arbitrariness of biblical morality does not, however, preclude an actual and true objective morality. We are all objects as well as subjects. Our needs can be observed rigorously as well as our resources, and matching the one to the other is not a matter of subjective and arbitrary desire.
Theists could well consider this problem a gift of god, as it could be understood as a challenge given us to use the means with which it endowed us to find a global, truly objective morality with the only universal tools we have: logic and science.