In my view, to be a genuine Christian, you must believe Jesus Christ died to pay the penalty for their sins. Who REALLY believes and who doesn't, I leave to God to judge. Those who do not believe will spend eternity separated from God, NOT because they don't believe, but because they have Sin that wasn't paid for, and God, being a righteous Judge, cannot allow that. I don't take the fire literally, I think its symbolic of the pain and regret of not having accepted the message when you heard it. I do not know precisely what happens to those who have never heard at all, but I suspect that everyone will be able to choose at some point, if not in this life than after. I do know, however, that the more knowledge you had in this life, the more you will suffer after death.