Statesboro, GA, USA
Though revelation plays a major role, I would have to say that a literal history (over against mere fanciful story telling) is an equally important part of the difference.
That's at least what I believe sets the Christian faith apart from the older paganism. I think the Gospel narratives are not easily dismissed like the Greek stories of their "gods". In fact it's a whole different style of writing. Consider what C.S. Lewis wrote, concerning this difference, in an essay entitled "Modern Theology and Biblical Criticism":
... Whatever these men may be as Biblical critics, I distrust them as critics. They seem to me to lack literary judgement, to be imperceptive about the very quality of the texts they are reading. It sounds a strange charge to bring against men who have been steeped in those books all their lives. But that might be just trouble. A man who has spent his youth and manhood in the minute study of New Testament texts and of other people's studies of them, whose literary experiences of those texts lacks any standard of comparison such as can only grow from a wide and deep and genial experience of literature in general, is, I should think, very likely to miss the obvious things about them. If he tells me that something in a Gospel is legend or romance, I want to know how many legends and romances he has read, how well his plalate is trained in detecting them by the flavour; not how many years he has spent on that Gospel.
... I have been reading poems, romances, vision-literature, legends, myths all my life. I know what they are like. I know that not one of them is like this. Of this text (referring to the gospel of John) there are only two possible views. Either this is reportage- though it may no doubt contain errors- pretty close up to the facts; nearly as close as Boswell. Or else, some unknown writer in the second century, without known predecessors or successors, suddenly anticipated the whole technique of modern, novelistic, realistic narrative. If it is untrue, it must be narrative of that kind.
However, that amazing possibility of a "myth" being written during that time, in the guise of historical narrative, is still a possibility. Therefore the questions surrounding the veracity of it's history are still to be asked. It's just that the alternative theories (the reconstructions which would deny the Biblical historicity), don't hold as much weight as the text as they stand, taken at their word. The reconstructions seem more "mythical" in the sense of creating more historical problems than they solve.
But I do admit, there is also a similarity to "myth" that the Christian faith has which is undeniable. Lewis himself was drawn to J.R.R. Tolkien's explanation of Christianity as "The myth which also happened to be true". Both greatly influenced by the beauty and ability of myth to resonate with "truths" in the human heart, they were drawn to Christian faith not merely because of it's literal and prosaic truth, but because of it's poetic truth. It seemed for them to ring equally strong in both spheres. Only in the ancient paganisms, it was always one sphere or the other.
Pardon me for one more quote from "Jack" ... I really don't mean to quote Lewis to death (though I know I quote him more than anyone else), but I just happened to read these things just today about his views on myth, before even seeing your thread. So I wanted to at least share the main idea of what I read, so well fitted for this thread (at least in my estimation) ...
Now as myth transcends thought, Incarnation transcends myth. The heart of Christianity is a myth which is also a fact. The old myth of the Dying God, without ceasing to be a myth, comes down from the heaven of legend and imagination to the earth of history. It happens--at a particular date, in a particular place, followed by definable historical consequences. We pass from Balder and Osiris, dying nobody knows when or where, to a historical Person crucified (it is all in order) under Pontius Pilate. By becoming fact it does not cease to be myth: that is the miracle.
(from the essay "Myth Became Fact")
So some find it is the hardest to believe because it IS so similar to the "ever after" kind of stories they've always wanted to believe, but couldn't. So similar, in fact, that the marked difference may be missed or skeptically denied. Oh, but if it really could somehow be true, then there was, after all, some reason we all loved the fairy tales. There was, after all, a spiritual and soulish reason that we all rejoiced when the hero, having saved the fair kingdom and left the dragon's carcass smouldering in the valley, was crowned with glory and honor.