God's book is reality itself. Your conscience, your ability to observe, analyze and judge. that is God's holy book. No written book is inerrant or divinely revealed. What makes a book profitable or effective in guiding you closer to God is its principles, the patterns of thought and behavior that a book commands or at least encourages the reader to adopt. That's what makes a "holy book" good. If the book encourages people to adopt destructive patterns of thought and behavior, that undermine life, increasing chaos i.e. entropy, then that book is evil (leading to a chaotic, worthless state and death).