To continue my previous argument,
I worded my comment very, very specifically. To recap:
The only way to make sense of an ought when it comes to morality is self-interest.
This is the only way to impose an obligation on us.
Ideally, we do things for God because we love God. This is what it means to become a Saint. We strive to reach that point, where everything we do is to further God’s glory.
But for us to be obligated to do something – in other words, for a law to be moral – there need to be consequences for it, or else there is no obligation.
Let’s use a basic example. I lie and say I won the lottery. I collect the money, then live out the rest of my life in luxury, even becoming a generous philanthropist.
Let’s say I’m an atheist. Now why should I care? “Just because?” Because…what? Are there going to be any consequences for breaking this moral law?
Seems like there aren’t any consequences, so as far as I’m concerned there’s no meaningful sense it’s wrong. So there can’t be moral laws.
The problem is there though, and it’s this? We can deduce moral laws. So if an atheist does this, what are his options?
- Come to the conclusion he’s wrong and there are no moral laws after all, or,
- Conclude that there needs to be a lawgiver that created the law and gave us a reason for following it, namely, consequences. And so, the atheist becomes a theist.
So, the honest atheist must be a nihilist.
(Of course, we find many moral atheists, because the moral law clearly does exist and they’ll jump through hoops figuring out how to justify it without God.)