You present the Bible as one text composed at one time, but I’ve never known anyone to take that view. The Bible can’t “take itself incredibly seriously” because it spans millennia in time, including at least a hundred years after Jesus. Hundreds of years after that is when “The Bible” as we know it today was even assembled from pieces during unification. Before that, early Christians had hundreds of religious texts and through a process of negotiable, brought them together under the Roman state. I’m sure if you read something like the infancy gospels which are not included in the Bible, you could probably also find similar themes.

Of course the stories remained culturally relevant through oral traditions and Jewish law. The common thread is culture and the stories of a people.