You're not looking for historians, you're looking for Biblical scholars, but you don't even need that.
The long and short of the Bible is, God created the world, but He was a jealous god, so he flooded the world after he got sick of sin. He decided that was maybe not the best course of action, so He instead sent His son to die for the sins of Man. That's pretty much it, with a lot of little details and contradictions (because, like the other comment says, humans wrote it).
But the answer to your question is, different managerial styles. In the Old Testament He tried to rule by fear; in the New, by love.
Capitalisations because that's how the people who wrote it pronoun God.