I have been an atheist since about the age of 12. Once I realized that, I went to science, and am now a biochemist and a neuroscientist. Having thought about this issue quite a bit, over what is now a long span of time, I've come to the conclusion that the specific belief in "god" is not really the most important philosophical concept; I think the belief in a soul is.
People talk about whether they do or don't believe in god, and many people, especially evangelicals, completely reject all those who do not. I have always been very curious about people's use of words, and exactly what it was they meant by them, even simple words like 'the' and 'is.' (There is actually a branch of philosophy devoted to this study.) Listening to people talk about their belief in god, and their arguments/discussions with those of us who don't, it seemed to me that some people meant it only as a source of moral guidance, and most of them, and nearly all the others, meant it as "that which explains that which I don't understand." This latter point seems likely to be behind the effort of evangelicals' decision to try to interpret the bible literally, as best they can.
This approach also helps explain why, the more people know, the less they rely on religion (e.g. the majority of the members of the National Academy of Sciences are non-believers. Membership in this organization, in the U.S., is the second highest honor a scientist can receive, second only to the Nobel prize).
Further, after one decides that the notion of god is mainly a way to explain things, the main question is where the world-wide need to believe in it is so common. Freud believed it was because people needed to feel taken care of, as they were by their parents as children. I suppose this does explain a large part of the need for religion. But, at least among the more mature and more thoughtful believers, my supposition is that there's another reason, which is the need to believe in a soul, and they explain that by its being a gift from god.
Belief in a soul is quite ancient, from well before christianity and possibly well before religion. It is the simplest way to explain the continuity of a person from infancy to old age. The concept has been used by philosophers of various kinds for centuries, in many different ways. Plato (Socrates) believed that souls were eternal, entering the body at birth and leaving again at death. Mormons have a very similar view. Most monotheistic religions believe in a soul starting near birth and departing for greener pastures at death.
But many views of the nature of consciousness, and a great many clinical studies of various kinds of damage to the brain, leave some of us with the concept that souls do not exist. A persona is created, actually fairly gradually, as the brain develops, and can be changed in many ways over the years. That intrinsic persona, or central aspect of one's personality, is not static, but changeable. While there is certainly a core persona that persists for a long time, it can nonetheless be changed in small ways and large ones, ranging from learning new things to having a stroke or something worse, like Alzheimer's Disease. But once the brain is gone, or even a significant portion of it is gone, there is no more of the same persona. For example, this is why the entire debate about Terri Schiavo was so foolish. All of us who had seen her brain x-rays understood there was no persona there any longer. Only people who imposed a religious belief onto the facts of the situation created the controversy.
Therefore, as I said, I don't think a belief in 'god' is so essential; the main philosophical point is the belief in a soul. I have found that many 'enlightened' intellectuals, who consider themselves Humanists, agnostics or atheists, still stumble on this point.