If God, Jesus, the devil, angels, and demons were all real, we still couldn’t rely on the Christian Bible as gospal (pun intended) — it was written by humans, specifically men, who could have misunderstood or invented things. Think of it like the Snyderverse in Man of Steel: Superman is portrayed as a brooding, violent character — but that’s not his true nature. In Batman v Superman, Batman is straight-up killing people — also not his normal characterization.
So even if much of the Bible reflects real events or real beings, parts of it could still be distorted, exaggerated, or entirely made up by the people who wrote it down.
But when you look at things like canonization and other religions adding on (like Mormonism) it gets fuzzy. Yes, Christians believe that the Bible is the inspired word of God, but can you really be certain that each step of the process was 100% correct? You don’t think there’s any room for human error in canonization or translation?