Below is an excerpt from Rebecca Newberger Goldstein's 36 Arguments for the Existence of God: A work of fiction. It is an excellent intellectually-satisfying philosophical novel that I would recommended for all thinking readers:
"My last question to you, Professor Seltzer, is, what motivation for adopting the moral point of view can you possibly offer without a belief in God and immortality?"...
"Professor Fidley worries that, without a belief in God, people will act only for reasons of self-interest instead of behaving morally. But then what does he offer as the only persuasion to adopt the moral point of view? Concern for one's self, in this life and the next. Without this, he says, there's no reason to act morally. In the end, it's Professor Fidley who reduces morality to self-interest.
"And it's no wonder that in the end he has to fall back on self-interest as the ultimate motivation for morality. He can't see what can be morally compelling about morality, in and of itself. If he did see that, he wouldn't think that he needs God to magically inject the morality into morality. And since, according to him, there's nothing compelling about morality in itself, he also thinks morality requires some lash to punish us in an afterlife if we don't comply. So, in the end, all that he can appeal to are motivations of self-interest. In the end, all that he can offer people as a reason to act morally is for them to act in their self-interest, currying favor with an authority that can dole out rewards and mete out punishments.
"But if the moral point of view is something that we humans can, with a great deal of effort, reason our way into, then morality itself provides the motivation to be moral. The reason to do the moral thing is that it's the moral thing to do; to do anything else is to make a shambles of our thinking, of our values, of our mattering. Our seeing for ourselves why it's the moral thing to do is what compels us.
"When we're trying to teach a child why it's wrong to pick on another child, do we say, 'It's wrong because if I catch you doing it again, you'll be spanked,' or do we, rather, say, 'How would you feel if someone did that to you?' And when we're wrestling with our own conscience, do we think to ourselves, 'If I do it, then I'll be flambéed in hell's fires,' or do we think, 'Would I want everyone in the world to behave this way? Wouldn't I feel moral outrage if I learned of someone else doing this?'
"... if we can't live coherently without believing ourselves to matter, then we can't live coherently without extending that same mattering to everyone else.... There are truths to discover in that process, and they're the truths that make us change our behavior. To assert that there has been no cumulative progress in discovering moral truths is as grossly false as to say there's been no cumulative progress made in science. We've discovered that slavery is wrong, we've discovered that burning heretics in autos-de-fé is wrong, we've discovered that depriving people of rights on the basis of race or religion is wrong, we've discovered that the legal ownership of women is wrong.
"Religious impulses and emotions are varied. There are expansive, life-affirming emotions that can find a natural expression in the context of religion, which is why I can never offer a wholesale condemnation of religion, even though Professor Fidley seems to think I do. But when religion encourages what I can only describe as a moral childishness that blocks the development of true moral thinking, then I do condemn it. When religion tells us that there is nothing more we can say about morality than that we can't see the reasons for it, but do it if you know what's good for you, then I do condemn it. We can do better than that. We can become moral grown-ups. And if there were a God, surely he would approve."