personally I believe spirituality is built into all humans...this is why so many have some belief in a God/gods of some sort.
Even those who dont believe in God/gods, they do believe in something that caused our being, ie evolution....this shows that even if one doesn't believe in a God/gods, they still yearn for knowledge, meaning and wisdom. We all do this because IMO we were created in the image of God and therefore we possess his qualities and creative ability.
So besides the bible, faith/belief is a part of our nature. And how we choose to exercise that need is a very personal thing based on our perceptions,life experience and environment.
I think that
curiosity is a part of our inherant nature, and that faith is simply one way to sate that curiosity.
We've always asked the Big Questions - where do we come from? Why are we here? Is there a purpose to all of this? Why do bad things happen, especially to good or innocent people? Etc. Faith is one of the ways that people answer those questions (I'd argue that it's not a
valid means to answering those questions, at least not with any accuracy since there is no tie to reality involved in faith, but that doesn't matter to most people).
The natural response when one of those Big Questions is unanswered seems to be "speculate." This has given rise to a massive variety of mythology over the course of human history that was made up to answer questions people of the time had no way of answering accurately. The Sun was Apollo's polished chariot wheel. God made man from dust. Bad things happen to you because of sins committed in your previous lives. Sacrificing a human being each day ensures that the Sun will rise tomorrow.
We all want those questions answered. In the modern age, we have a far greater ability to derive some of those answers from natural evidence rather than our own arbitrary speculation. We can test our answers now, and ensure that they accurately reflect reality. This has led to many faith-based answers simply disappearing - nobody actually believes that the Sun is Apollo's chariot wheel any more, because we have found a
real answer to that question.
Some questions, however, still can't be answered. The existential questions like "why are we here?" don't seem to have any objectively determinable answer. Many people (most?) still find the answers to these questions through faith, simply because there is no way to truly answer them.
The division between "fundamentalist Christians" and "moderate Christians" seems to be that fundamentalists (like you, Peg) seem to believe that faith-based answers to
all of the questions are superior to even those that have been answered by modern science (ie, Genesis is literally true and the Theory of Evolution is false), while "moderates" hold only to those answers that science is unable to provide (Genesis is allegorical, the Theory of Evolution is accurate, but God still dictates the purpose of our existence, Jesus rose from the dead, etc).
I think that it's the desire to answer those questions that causes people to cling to faith. So long as the Bible answers at least some of those questions to greater
personal satisfaction (regardless of actual accuracy) than other sources, people will continue to believe it holds special significance even if some of those same people discard large segments of the Bible as factually inaccurate.
Personal satisfaction is the key, however. It's what allows the moderates to maintain faith even with no
real reason to do so. It's subjective, it's arbitrary, and it's wishy-washy, but regardless of the relative
accuracy of two potential answers, most people will still choose the answer that is most
personally satisfying. Given that either a) when we die there is nothing, just as before we were born and we cease to exist or b) when we die we go to a heavenly afterlife forever, most people will choose b) - not because they have any objective reason to think that b) is more accurate, but because b) is more personally satisfying. It really does sometimes come down to a subjective determination of personal preference - people will treat reality in the same way they treat arbitrary personal value determinations. Why Christianity over Islam or Hindu or Buddhism? "Because I
like Christianity better." That this personal comfort level is typically due to cultural familiarity and has nothing to do with anything factual or objective is irrelevant to the choice.
But that's just my take. This question is extremely complicated to answer - I imagine that there are nearly as many reasons behind the faith of moderate Christians as there are moderate Christians...and that many or even most may be unaware of their own motivations. Many of them, like me before I began critically examining my own beliefs, simply never even think about it.