There have been several conversations in the blogosphere (sorry, I'm too lazy to link) about the source and foundation of morality, and specifically about whether morality has a divine or a naturalistic source. I just can't get interested in this (despite this post), perhaps because this strikes me as a false dichotomy. Certainly, evolutionary biology may offer interesting accounts about the natural history of our social norms and gut reactions, but this does not justify those norms or reactions. (It may help us in thinking about how to overcome or modify normative behavior and inclinations that we judge to be no longer trustworthy or, indeed, ethical. It may help us understand why, psychologically, we often judge as we do.) On the other hand, I guess Plato's Euthyphro pretty well convinced me that it's implausible to hold that X is good (or right) because the gods love (or command) it. I can understand the idea of God as an "ideal observer," who has a perfect understanding of the good and the right (and the virtuous), but such a conception doesn't help us justify any particular moral claim because we are not the ideal observer (and can't know how the ideal observer would judge).
Of course, some hold that there is no reason to "be moral" if there is no God, and thus that the basic reason to be motivated to act morally is divine in nature. But I think there are cases where the idea that we "need" a reason seems strange. Do I need a reason to love and care for my children? Indeed, would warning me that God will punish me if I do not make me love and care for them more? If the question then becomes, "But what is the point of doing one thing rather than another, if there is no eternal reward or justice in the universe?" I would be inclined to respond that some of the "rewards" are internal to the relationship itself, and some arrive when you see your child becoming a marvelous person. I would also suggest that anyone who's worried about "what's in it for them" probably shouldn't have children in the first place. For the most part, it isn't about you. Christian ethics generalizes this point in certain ways (as does the Buddhist ethic of universal compassion). "It" is about no one and everything. I guess I might say that "it" is about being in sustained (and sustainable) harmony with the universe. (That's a bit abstract, and a bit hippie-ish.) There are surely different ways of doing that, but there are also surely many ways of being out of tune. Seeking a reason to live a decent, dignified, and beautiful life ultimately doesn't seem much different from looking for a reason to get out of bed every day. But I'm sympathetic with the thought that things can matter now even if they don't matter "forever" (or, "in the grand scheme of things"). The person in search of a reason to "care" shouldn't be given a reason; there may be no ultimate reason. Rather, they should be shown how to care for something, or given something to care for, in a way that may restore their sanity and, with that, their capacity to understand and imagine the possibility of a basic (and in some ways unreasoned, unintellectualized) love, care, and respect for other things.