Why do you think this?
Because if you believe in God,you take it for granted like the air.
Air is required for us to live. But nobody mention it and air is in EVERYWHERE.
God is like air,isnt he?
Then why they always mention him? Because they doubt the existance and insecure about it.
God is almighty. But All the christian believe that they can commit sin.In spite of ALL THE EXISITANCE OF THIS WORLD IS GOD, those christian claim good and bad arrogantly. If Bad exists,it means God fail. No way. The history of creature is millions years long. If God failed,we might havent exist.
Pure logic.