On December 15, 1998 the "Buffy the Vampire Slayer" official posting board, series creator Joss Whedon provided some background on an episode of the show which featured some religious themes:
[...] Was it God? Well, I'm an atheist, but it's hard to ignore the idea of a "christmas miracle" here (though the PRAY on the marquee was an unintentional coincidence). The fact is, the Christian mythos has a powerful fascination to me, and it bleeds into my storytelling. Redemption, hope, purpose, santa, these all are important to me, whether I believe in an afterlife or some universal structure or not. I certainly don't mind a strictly Christian interpretation being placed on this episode by those who believe that -- I just hope it's not limited to that.
From an 09-Oct-2002 Onion AV Club article titled Is There A God? :
Joss Whedon is the creator/producer of Buffy The Vampire Slayer, Angel, and Firefly.
The Onion: Is there a God?
Joss Whedon: No.
O: That's it, end of story, no?
JW: Absolutely not. That's a very important and necessary thing to learn.
In the writer/director commentary track to Episode 16 of Buffy the Vampire Slayer Season 5 (The Body), Joss makes the following remarks concerning his characters' responses to death and mourning in general: "...at this time a lot of people turn to, as Tim Minear would call him, The Sky Bully, but since I don't believe in The Sky Bully, and don't really have that to fall back on, I haven't really found any lessons in death other than I wish it wouldn't."
In the commentary track to the Firefly episode, "Objects in Space," Whedon mentions that he came to the realization that he had no faith. He then goes on to describe how the themes of the episode, the physicality of things (and people) and their relationships to each other, how this materialism relates to human action and interaction. He also quotes from an Angel episode that if nothing we do in this world matters, then the only thing that matters is what we do.
Perhaps someone can flesh this description out? I wrote this from memory while at work...
The whole episode seems to be a nod to existentialism and phenomenalism, particularly the writings of Jean-Paul Sartre. Joss makes a couple of references to one of Sartre's works, Nausea, and - to quote the episode - how people "...miss out on what's solid, the substance of things... objects in space." He talks about how objects are so vividly real, referring to the bouts of nausea suffered by the main character in Sartre's work, and that this realness is what Sartre meant with his idea of "existence precedes essence". Objects are real, existing in and of themselves, with no higher order giving essence to them. This leaves open the idea that the essence of an object is what we bring to it - in a larger sense, that the essence of life is what we bring to it, not something predetermined or higher order. Joss displayed this (damn cleverly, I didn't notice half of the things in this episode until I watched the commentary...) with River picking up Jayne's gun and seeing a branch, something harmless. In her hands, around her friends, that's what the gun is, that's what she brings to it, in that situation that is its essence. Morally, this is where the Angel quote comes in, our acts exist, not driven or judged by a moral law or a divine order, and so they are what we bring to them. In short, what people do matters. And it matters because it really doesn't. "If there's no great glorious end to all this, if nothing we do matters -- then all that matters is what we do. 'Cause that's all there is. What we do. Now. Today." I think the message is that we almost have to make our acts mean something, because otherwise we're left with the gaping abyss of nothingness, which is - as Sartre would put it - anguish. Can't speak for Joss, but Sartre was arguing against determinism, of all kinds, anything that would place a constraint on human spirit and consciousness. It's possible that God or religion could be conceived of as such - religion is almost always deterministic. We use it as an escape route from the horrifying nothingness that we'd have to face in place of it. Sartre coined the term "bad faith" to describe this, suggesting that it was a fallacy - through our immense freedom, we choose to perceive that we are bound by some objective moral code, or to a God, when really we are just doomed to freedom.
I also realise I just went off on one a bit. I'm very sorry.
In a Q&A-session while promoting his movie Serenity, Whedon was asked: "What do you have against being a Christian?" He answered:
I don't actually have anything against anybody, unless their belief precludes everybody else. I am an atheist and an absurdist and have been for many, many years. I've actually taken a huge amount of flak for that. People who have faith tend to think that people who don't, don't have a belief system and they don't care if they make fun of them. It's actually very difficult: Atheists are as a group not really recognised by the American public as people to be taken seriously. This does not mean that I rail against religion, however the meaning of life and the meaning of what we do with our lives is something that is extremely important to me. I have included characters from many different religions particularly in [Firefly], but also in the other shows as well, because I'm interested in the concept. I think faith is an extraordinary thing. I'd like to have some, but I don't and that's just how that works. [...] There's one other thing I would mention, which is from Angel actually: One of the few times I really got to sort of say exactly what I think about the world was in the second season of Angel, episode 16 ["Epiphany"] when he'd gone all dark, because he does that, and that he was getting better, and he basically decided -- he'd been told: "The world is meaningless, nothing matters." And he said: "Well then, this is my statement: Nothing matters, so the only thing that matters is what we do." Which is what I believe: I believe the only reality is how we treat each other. The morality comes from the absence of any grander scheme, not from the presence of any grander scheme. [...] So the answer is: "Nothing, unless you've got something against me."