Hi, I am about to give you a copypaste from /u/iopha about a year ago adressing this exact issues. He/she litterally could not have put it better so I thought it would be better to just let them say it.
First, off, though I am an atheist myself, I want to empathize a little: this must be difficult for you and your family. Your faith commitment is an important part of your life and it is bewildering to have your own child turn away from this. I don’t know exactly what you believe, but you might be worried about his soul in the next life, or his behaviour in this one. If you don’t believe in God, how do you know right from wrong? If you reject God, how will you be reunited with Him in the next Kingdom?
The most important thing to understand is that these kinds of concerns, while very vivid and real to you, only make sense within a belief system your son no longer accepts. There is no sense in making threats of Hell or damnation anymore: atheists do not believe such a place exists. We don’t believe such a place could exist. The thing that is important to remember is that while we no longer believe that there are places beyond the world, the world he lives in has now become all the more important. That’s all we have. That’s all we ever have. His world is family, and school, and friends: all these things structure his life and he will need them more than ever. He needs you. He’s still a kid, and he’s a kid dealing with Really Big Questions in the only way he can: honestly and critically.
Most of us have come to this point honestly. This must be emphasized. We’re not angry at God, we’re not trying to get attention or going through some cultural phase. We looked at the arguments on both sides and came to the best conclusion we could. We only have 70 odd years on this planet. We make mistakes, too; we are fallible creatures prone to error and haste. We do our best. And sometimes our best is ‘well, I don’t think any of this is right.’ I don’t pretend to have all the answers. I don’t rightly know where the universe came from, or how life began at first. But I don’t need all the answers to know that some answers are the wrong ones. I don’t know, and I don’t think Christians, or Muslims, or Taoists know either. They claim to know; I claim to not know.
Suppose I’m wrong. Suppose your son is wrong. I’m standing outside the pearly gates and St. Peter, or God Himself, gives me one chance to explain myself. What would I say except “I’m sorry–I got it wrong. I really tried. But I got it wrong. I saw all the different religions, each saying different things, all changing over time. It seemed just a part of human culture, not ultimate truth. I saw unnecessary suffering and couldn’t make heads or tails of it, if you were good and all-powerful. It didn’t make sense to me to posit something existing to explain existence: that gets it backwards. I’m sorry, God, that I didn’t believe in you, but it wasn’t malicious–I just–I just screwed up.”
What would Jesus say to that? Would he send me to suffer forever? Do I deserve to be tortured eternally because I read Lucretius as a young man–the 2,000 year old Roman poet who professed his atheism before Christ ever walked desert sand? Because I looked at the ontological argument and found it wanting?
Or would he press me to Him and forgive me? And wouldn’t I desire that forgiveness—?
If there is a God that would send me to Hell for making this mistake, I don’t want it in my life. Nothing justifies torture. Nothing at all. And He would not be worthy of worship–or even respect. If He is merciful, then I will apologize. If I am right–and he doesn’t exist–then I live my life as a free man.
And that is how atheists live: under actual freedom. The German philosopher Nietzsche wrote that ‘freedom is responsibility’–genuine freedom. I am responsible for the consequences of my actions. So: how do I live? What do I do? Do I want to live in a society where everyone does what they can get away with? What standards do I hold myself up to? This is the essence of the atheist’s morality: his freedom, his rationality.
Before even Lucretius wrote his atheistic treatise De Rerum Natura, there was another man, Socrates, who asked a simple and startling question: Does God say something is Good because it is good, or is something good because God says it is? We must be careful here. If what is good is whatever God says is good, then we have no morality at all, but caprice. If God says: kill your son! it is good to kill your son. If God says: from henceforth, children shall be murdered–then it is good, by definition, that children be murdered. But that’s not morality. That’s authoritarianism. And if you say: “But God would never do that,” I ask: why? Because if there is a reason, then goodness is independent from God after all. It is grounded elsewhere. In what? Well: maybe in reason itself? Or maybe morality is just part of the universe–a different kind of part, not like your sofa or TV or the moon is part of the universe, but the way numbers, or relations (like ‘equal to’)–an abstract object, none less the real.
There is a very, very long tradition of ethical thinking that is, in fact, older than Christianity itself. In philosophy classes we teach wisdom that was recorded a millennium before Christ. If it is impossible to be good without God, there wouldn’t be one virtuous atheist. Yet there are millions of us non-religious men and women on the planet, and we live our lives, as best we can. Atheists don’t fill the newspapers with tales of carnage or debauchery–clearly we can figure it out on our own.
Well. Not quite on our own. We have each other. No one else–just each other. And that’s enough. So be there for your son.”