Some people hear their own inner voices with great clearness. And they live by what they hear. Such people become crazy... or they become legend.
But I don't really care for directors flaring up and trying to humble some actor, which they would do to try and make an example out of them so everybody else would stay on the ball - and David wasn't anything like that.
The Bible should be taught, but emphatically not as reality. It is fiction, myth, poetry, anything but reality. As such it needs to be taught because it underlies so much of our literature and our culture.