Ok, in response to the "He shound already know if he's a Christian" argument...
I've run into many men who profess to be "Christian" and/or men who I've met in church who have sex like a horny goat. The fact that he says he's a Christian does NOT mean that he abstains from pre-marital sex. As a matter off fact, I've run into more church-going men who want sex than those who don't. In spite of their professed religous beliefs, not all of them understand and appreciate the value in waiting until marriage.
Furthermore, if you're in the early stages, then it's true that bringing sex up is probably not necessary.
But if you haven't had a conversation about spirituality yet, how do you know what his beliefs are? I mean, in theory, it's great to say, "Well I only deal with Christian men." But this, IMO, hinges on how you approach the topic of spirituality religion with men you meet in places other than church/religious functions etc.
Obviously you aren't assuming that every man is a Christian, so there has to come a time when you bring religion/spirituality up...or he does. Either way, it's very possible for him to want to make sexual advances before that conversation is had. Some women would immediately argue that if he's not a man of God, there's nothing to discuss, and that that should be one of the first things you ask, and I agree wholeheartedly, but IRL, it doesn't always happen that way.
So my thing is, I'm not gonna bring it up for the sake of bringing it up, but if I honestly believe he has plans of trying to bed me, I'm going to politely explain that I don't engage in pre-marital sex as soon as practically possible to avoid confusion and name-calling. And yes, he *should* know, but I don't like to leave things to chance. I'm big on communication so should he step out of line and try me, he can't say he didn't know or that I never told him b/c I "assumed." All of my cards are on the table so nobody's time gets wasted.