I've recently had cause to reflect upon what exactly I think the Bible is. Here's a working definition: a collection of writings from antiquity that happen to be true, and whose truth God intends to control when in conflict with other purported truths. Parse:
That the Bible is a collection of writings from antiquity is, I think, noncontroversial. I don't think I know anybody who doubts that the entire thing was written in the window of 1500 BC - 200 AD (to give a century's or so margin for error on both ends). It's worth remembering, though, that these are really quite ordinary documents - or, at any rate, more ordinary than the name Holy Scripture tends to conjure. The documents are extraordinary in that they existed at all (in the case of the narrative histories, for example, which were pretty clearly written at least a hundred years before Greek historiography really took off) and in that they are extant and in their content, but the actual form of the documents is relatively mundane. Narrative histories, records of prophecy, lyric sheets, poetry, and semi-personal correspondence - none of those types of documents are especially weird, with the possible exception of records of prophecy, and even those aren't weird in the context of antiquity. "Holy Scripture" is not a form of document I am very familiar with, and I don't have the intellectual tools to deal with it. But I know more or less what to do with historical narrative, lyric sheets, and letters.
Next, I believe that the Bible "happens to be true." I don't mean to say that it is true by accident, of course; I think it's true because God spoke true things and so orchestrated the course of human events that those true things remain extant. By "happens" I mean to convey that I think the Bible is true because I think it is true, and not because it is Holy Scripture, or The Bible.* That is to say, I think the Bible is true because it is true, and not because it is the sort of thing that must be true. Granted it was, I think, spoken by an entity that only speaks truths - but that makes the Bible exactly as true as if God were to speak the Pythagorean Theorem, at least as far as I can work out.
And then we get to the question of "true." The common question here seems to be whether one believes that the Bible is "literally" true or not. I don't think that's a particularly sophisticated question, and I dislike the way it seems to have become a political codeword. One gets the distinct impression when listening to somebody ask whether one believes that the Bible is "literally" true that nobody in their right mind could possibly believe that anything is "literally" true. Here are examples of things that I believe in quite wholeheartedly but probably less than what seems to be meant by "literally:" my own existence as a contiguous individual, my family's love for me, the existence of George Washington, the course of the Battle of Gettysburg, the fact that I know how to dance, and the evidence of my senses that I am presently wearing a blue shirt.
I hope that will dispose of the "literally" label. To continue in the same vein, I would say this: I tend to believe the Bible more the more important the statement in question is to the author's purpose. For instance, I quite doubt that the Philistines had three thousand chariots when they faced Saul at Micmash (1 Sam. 13:4-6). I just don't see how the logistics of that would work, and it's wildly outside of military historical precedent. And because the author does not seem to be noting the size of the Philistine chariot arm as miraculous I am inclined to believe that somebody, at some time, made an error.
Contrast that with an episode where the author is plainly attempting to relate a purported miracle, such as the consumption by fire from heaven of a waterlogged bull upon waterlogged wood upon a waterlogged pile of rocks surrounded by a moat filled with water (1 Kings 18:30-38). That sort of thing strains credulity, to be sure. But in this case, the author is plainly aware that what he relates seems impossible, and is writing it down precisely because he is aware that it is an extraordinary event outside of normal human experience. Or at any rate that seems to me to be his perfectly obvious intent. It does me no good, in that case, to say that such an event is so outside of normal human experience that I will not believe it happened.
Now of course I might say that the author's obvious intent is to be allegorical, and many people do. In the face of reasoned and reasonable literary analysis to that effect, I'm perfectly willing to believe that a given passage of Scripture is allegorical. It is, after all, simply an ancient document. But it seems incredible to me to believe that the default for ancient writers was to be allegorical when they discussed miracles, as if the majority of the ancient world shared the modern skeptic's assumption that such things Simply Don't Happen, or have to have happened a hundred times before they can happen once.
And of course when I discuss "truth" in this context I mean something more than a recitation of historical facts. I think it is pretty plain that the Bible teaches that there is no entity equal to God, that the Holy Spirit is a person, that men and the natural world are not as they should be, or that neither men nor the natural world can be as they should be except through Jesus Christ, or that not being as they should be is pretty much the most terrible thing in existence. Those are factual assertions, but not of the historical kind, and they are the sort of assertions that I think the Bible is really much more concerned about than whether Elijah was "literally" taken into heaven by a chariot of fire or whether Mary was "literally" a "virgin."
Which brings us to that truth being controlling. I think Lewis had it right when he put it this way rather than some of the other, more common formulations. The Bible does not really make any factual assertions at all about chemistry, for instance (or at least, I don't think it does). Consequently I have no trouble at all believing what my chemistry professors tell me about the behavior of atoms and molecules (subject to the usual skepticism anybody should bring to academic assertions). On the other hand the Bible does quite clearly assert as fact that there is no entity equal to God. Consequently I have a good deal of trouble believing anybody, or any part of any religion, who tells me differently.
In addition, I think that the Bible is set above other assertions which may be "true" in the ordinary sense (this sense, combined with the previous sense of the Bible being controlling, comprise the greater part of what I mean when I say that the Bible is "holy"). For instance, the Bible does not explicitly teach me to be gentlemanly. It asserts as true fact that I ought to be kind, and good, and compassionate, and loving. But as for whether I should afford women more social rights than men, or treat them with separate but equal courtesy, or uphold my personal honor or that of my family name ... well, all of those are (I assert) good ideas which will profit me and those around me. But they aren't Biblical. They aren't the same level of true, if you will, as that I should be kind and good and compassionate.
* Precisely why I think the documents are true is outside the scope of this post.