"She's treating it like it's true. But isn't it just a myth?"

One of the confusions that has come up during our reading of Karen Armstrong's A History of God is whether or not the Bible is a reasonable historical source, and whether the author thinks the Bible is true, and whether or not one has to believe it is true to find her conclusions valid.

Is this Myth True?

One of the first things a student of religions is taught in an academic setting is that the definition of myth is "a true story".  Not because you must believe that it's true in order to study it, but because the members of the religion believe it.  The study of religion is not the study of God or Gods (that would be theology) or the structure of the universe (that would be physics or metaphysics), but the study of the history of the beliefs of a culture.  It's important to understand that they believe it's true.  Religiously motivated self-consciousness, decision-making, and cultural identity can only be understood within the context of the believer's belief structure. Jack Miles said it very well in the first line of his "God: A Biography":

That God created man in his image is a matter of faith; the man has spent centuries trying to emulate his image of God is a historical fact.

Is the Bible a Historical Document?

Yes! It's historical in more ways than one.

First, it's grounded in real historical places and many of the main characters are known historical figures. The Bible is not pure fantasy, as say the fable of the Tortoise and the Hare are.  It's the primary historical narrative of the people of Israel.

Second, it's historical in that it has been revised, redacted, and added to over many hundreds of years, each time incorporating the evolving beliefs of culture at the time the redactor lived.  The Documentary Hypothesis examines this in great detail.  Genesis 1-2 are retelling of the Babylonian creation myth, written by exiled priests of Israel.  The Exodus stories of Moses clearly reflect moral values of the Israelites hundreds of years later.

So...

The correct question to ask is, is it a factual document?  To that, the answer is clearly no, not purely factual.  Abraham and Jacob were most likely tribes, not people.  Joseph is not likely Jacob's son, but the name of a tribe come out of Egypt, bringing their cult of Yahweh with them.  The mixing of tribes in Canaan resulted in a synthesis of El Shaddai, Baal, and Yahweh to form the God of Israel.

The text clearly has an agenda: to capture the religious history of a people in a way that not only provides them with a common identity, but also cultural direction for the future.  Abraham and Jacob most likely did not worship the same God, but they became a single people and so their gods became merged in their collective understanding of Israel's religious identity.  The laws of Moses, written centuries after Moses died, give the weight of religious authority to moral and behavioral codes that Israel needed to maintain it's identity so many years later.  The words of the prophets provide a sense of cultural identity to a people in exile, and a positive outlook on their future.

That the Bible records and reflects the religious identity of a people is exactly what makes it true.

Further Reading:

Jack Miles, God: A Biography.  This is a literary analysis of the character of God throughout the Old Testament.  What makes it relevant here is that Miles is very careful to call out exactly which of God's many names are being used in each story, and how the attributes of God in each story provide clues to the factual origin of the story.

Karen Armstrong, The Great Transformation.  Pgs 38-41 provide a factual historical perspective on the various origins of the people of Israel and of their Gods.