Because we never will know everything, we all need to believe.
Free world people know that we all need believing. And that being conscious of this fact is an essential ingredient for building a peaceful society.
Stories in books synchronize believes but never can be "the truth" or "the law" because if words would be the truth, we all would speak the same language.
We (humans) believe for we can not know everything.
Some of us may need to personalize our believe in gods or one god.
We "Free world people" give every individual the freedom to believe what they need and expect every body to respect all forms of believe.
Believing is the opposite of knowledge. Also when it is written in books. We can tell each other stories to synchronize our believe systems, but we have to respect any individual deviation from what we think as being common believe, because believing is individual. It is a form of the highest respect for the individual to accept that we do not all know the same things, and therefore can not have the same believes. This respect for each individual beliefs is Free Humanism. And it is personal and thus never can be in books.
Religious books are about traumas of humanity and rules for live learned from that. Traumas like famines, droughts, plagues and so on. But unfortunately also about how to deal with other peoples. Sometimes even about the right to kill other people on religious grounds. These religious books remain relevant for the lesons learned by humanity, but are outdated for their science, truths and laws, because humanity kept on learning after the books where written. They freeze humanity into the past and can only for a small part can prepare for the future. These religions are at war with each other for ever because they stopped learning.
We (humanity) now live in a global connected world and learn permanently. We change the fabric of our society every day.
We now should have learned that religious laws can be a source of inspiration, but never can be "the law" for the future of humanity.