There are some assumptions built into the conceptualization implicit in the OP and some responses that need highlighting and discussing, IMO.
First, let’s note, and toss to one side, the fact that a minority of Christians believe in the literal verbatim inspiration of God – that he in effect dictated the Bible to human writers who acted basically as stenographers, or at best put into their own wording the ideas he’d told them to say. Some of the psychology outlined by people above has a lot to do with why this view is held, along with a point I tend to stress: insecure people need to have something to cling to, and an inspired, inerrant Word of God unchanging across the centuries is something that fills the bill for their needs.
Now, to deal with the others, let’s start with a parallel:
The Iliad is an epic poem by Homer dealing with the siege of Troy. In point of fact, there were Greek attacks on Troy, several of them. It does have a historical analog. And its heroes are legendary, but at least a few families in historical Greece claimed lineal descent from some of them, implying that there were historical figures on whom the characters of legend were founded, though of course a lot of fiction was added to them.
But we also have Greek gods getting involved. Ares and Diomedes fight and Diomedes wounds Ares. Surely that’s fictional? Well, yes, of course, but the fact is that beyond what we can learn about Achaean customs and traditions, we also get a handle on how the Greeks of Homer’s time conceived of Zeus, Ares, Aphrodite, etc. That is, it’s a valuable resource in the study of Greek religion.
Likewise, Abraham, Moses, David, etc. are figures of legend. Who they are, what they did and said, are reconstructed in mythological and legendary terms. To what extent they were real people underlying the legend is debatable. And of course we get a handle on Jewish custom and tradition across a broad time range.
In addition, the Bible is a valuable resource for how the Israelites and Jews conceived of YHWH at various times in their history. That’s valuable information in and of itself.
But beyond all this, let’s make, for the sake of argument in this post and responses to it, the presumptions: there is a God, a being transcending this Universe who was its Creator. This does not automatically presume that the first chapter of Genesis is a verbatim account of how He did it (it shows every evidence of being myth) but merely that He did. Further, that this being relates to humans interpersonally, as Person to person, and takes an interest in what they do and why – and that, for reasons best dealt with elsewhere, He took a special interest in the Children of Israel and their descendants, and used that one-on-one contact to teach and guide them. That does not necessarily mean that any one of them got it right, relayed precisely what He wanted them to say. It does mean that we can gain some knowledge of Him by following the evolution of Israelite/Jewish/early Christian conception of Him as it is recorded in that collection of writings put together over time.
And that makes it an extremely valuable resource, even without any assumptions about its inspiration.
Note what I’m saying here: not that any rational thinker has to buy a pig in a poke about Christian belief, but rather something syllogistic: there are people who believe in the Christian God, and not all of them subscribe to turn-off-your-brain dogmatism about the Bible. IF they are correct about the existence, characteristics, and methodology of the Christian God, the Bible becomes a valuable resource for learning about Him – when one extracts the knowledge from the cultural matrix in which it is embedded.