Lately I have read a few things about "who wrote the bible" aka the documentary hypothesis, refutations of it and such things. I am not sure what I believe and I haven’t researched it enough to offer any opinion. What I want to talk about is the question whether it really matters.
So the basic dispute is about whether the Torah (the five books of Moses) was written by one person (Moses), or by several (at least four different people). I think there are two questions to be asked: If it were true that the Torah was written by several people, what would that say about (a) its relevance, and (b) its divine origin.
So, first let’s look at relevance. Would the Torah be automatically irrelevant if written by several people? No. Books written by several people can be relevant. There is no one claiming that the entire Tanach or the Talmud was written by one person. Both books are still pretty relevant for most Jews. Christianity bases the faith of Jesus on the gospels and there are four of them, written by different authors. I don’t think anybody claims they were written by the same person. They are still the basis of the faith in Jesus. So no, single authorship is no requirement for relevance.
What about divinity? Does "divine" mean "single author"? I don’t think so. Tanach and Talmud are not just any books, they are divine (maybe it’s not the same level of divinity as Torah, but still). For Christians all four gospels are divine books. I’m sure there are other examples of multi-author revelations in other religions. If G-d can inspire one person, he can inspire several persons. Even if instead of "inspire" we use "revelation" in the sense of G-d dictating every word, there is no inherent problem. There are Christians who believe that every word of the bible was dictated by G-d (Verbal dictation). This definitely means G-d dictated to different people, but surely G-d can do that. So no, a multi-author document can be divine.
To summarize: Having multiple authors does not in itself make the Torah irrelevant or the work of mere humans. Unfortunately most proponents of the documentary hypothesis present it in a way that at least implies one of the two points. But this doesn’t mean this is a justified conclusion.