Christians don't belive the Bible was written by God they belive it's the word of God. the inconsistencies and contradictions are because its been written by many people over hundreds of years.
They don't even believe it's the word of God, strictly -- Jesus is the Word of God, the Bible merely contains (in parts) the word of God as reported by men. This is a key distinction between Christian and Islamic theology.
I've heard it described as "Jesus is the Word of God, the Bible is words about God", but there is definitely diversity of belief within Christianity about that; there are certainly groups that have views of the Bible that other Christians view as near-idolatrous.