If God wanted us to have a complete manual for living, he would have given us one. If the bible were such a manual, it would not be full of contradictions, errors, and forgeries. And it would not be available to only a small fraction of mankind.
Life is difficult and complex and human beings are the most complex thing in the universe. We want to know what to do and we want to know that someone or something out there cares about us and has a purpose for us. And we want it put into words.
But the truth is that such texts were not handed down by God. They were written by people who had various purposes for what they wrote. Some of what’s in those texts is true, but like anything done by humans, they are flawed and incomplete.
Most things done by humans can be improved over time. Especially as more people contribute their ideas. Many of the flaws can be ironed out. Can religion be improved? Can our understanding of God evolve? I would argue that it can and that it has. More and more souls are being added to the planet. There are many more souls who are having their own experiences. And the tools of science help us better understand the nature of reality (or at least our perception of it).
Is it rational to believe that our understanding of virtually everything can evolve, but not our understanding of why we are here and how to live while we are here?