They are 66 books - biblia, as they were originally called. They interpret each other.
And often they contradict each other. Sometimes a prophet
knowingly contradicts another, concerning some important religious practice which is taken for granted as being in accordance with God's will. Take Jeremiah 7:22 on sacrifice, for instance:
"For in the day that I brought them out of the land of Egypt, I did
not speak to your fathers or command them concerning burnt offerings and sacrifices."
This of course has implications for Pauline Christianity, where Christ himself becomes the sacrifice offered up.