From the preface of James Kugel’s Traditions of the Bible: A Guide to the Bible As It Was at the Start of the Common Era:
We like to think that the Bible, or any other text, means “just what it says.” And we act on that assumption: we simply open up a book–including the Bible–and try to make sense of it on our own. In ancient Israel and for centuries afterward, on the contrary, people looked to special interpreters to explain the meaning of a biblical text. For that reason, the explanations passed along by such interpreters quickly acquired an authority of their own. In studying this or that biblical law or prophecy or story, students would do more than simply learn the words; they would be told what the text meant–not only the peculiar way in which this or that term was to be interpreted, but how one biblical text related to another far removed from it, or the particular moral lesson that a text embodied, or how a certain passage was to be applied to everyday life….
And so, it was this interpreted Bible–not just the stories, prophecies, and laws themselves, but these texts as they had, by now, been interpreted and explained for centuries–that came to stand at the very center of Judaism and Christianity. This was what people in both religions meant by “the Bible.” (pgs. xviii-xix; you can read the whole preface here.)