Atheism seems to me to be the sensible point of view in the universe I live in. (Imagine a long discussion of why I think this is so, though you may reduce it to Occam's Razor.) In the universe of Buffy and Giles, the rational person reaches the opposite conclusion. This isn't a matter of faith. Gods aka Powers exist and there is proof of the nice solid scientific falsifiable-theory sort. The human soul exists and can be detected and interacted with.
What does it feel like to be an instrument of one of the Powers in some long war against demons? What's it like to be pissed off about a real, concrete example of a diety allowing bad things (stress of Slaying & early death) to happen to a good person (brave, selfless Slayer)?
My story complicates things a little by getting the Power aka God involved directly, and making it quite clear to Giles that He/She/It/They/Insert Pronoun is taking a personal interest in this Slayer and doing things to help. Which gives Giles a wiggins. And there's some more I'm thinking about (reluctant surrender to destiny, fears about what being a god's instrument is going to do to him, questions about the rituals of organized religion, and so on) but I prefer to work it out in the fiction instead of here.
Nice solid SFnal topics. Big fun. Way too ambitious for a first Buffy project but I ain't letting it slow me down. I'll probably finish the Holmes thing first, though. So I observe the payoff: my attempt to get myself writing again has worked. I took away all the danger by doing it anonymously (nobody who knows me can care) and by writing fanfic (it's all just a pastime, so nobody really cares anyway) and woohoo. I may yet recover from the stupid, stupid decision to go to that 6-week writers bootcamp thingie.