How Could You Be So Heartless?

Lets all take a moment to reflect all the evils in the world. In my book the girl is beaten by her father for no reason. I mean FOR ABSOLUTELY NO REASON AT ALL. If she even looks at something the wrong way he will just whip off his belt and really beat her. Her only escape? Going to her secret hideaway in which an escaped german prisoner is hiding. Actually she is Jewish. And the prisoner is a Nazi. How is it that a Nazi (her only friend) is so nice and sympathetic and her own JEWSIH father is so cruel? I don't understand it and actually in the book neither does he. Does anyone really understand it?