One thing....I wanna defend the protaganist. Some have suggested that he's an inept coward....too weak to stand up for himself. But this is only half the story. He is also brave for acting in accordance to what he perceives as his responsibilities.
Why doesn't he knock out the man sleeping with his wife? Well, such an action may serve to satisfy one's jealousy/anger....but doesn't serve the best interests of one's family.
Why doesn't he turn in his bribing student? Well, such an action may serve his hopes of getting tenure....but doesn't stay true to his role as teacher to student.
But watching the movie, you get the sense that he's hiding behind the 'altruism' and 'righteousness' of his actions to avoid laying claim to his identity. He is a moral man...but he also uses those morals to hide. He's inactive, overly-passive.
He doesn't HAVE to act out cause such an act would be selfish....against God's will. Underneath that theme, he also doubts God's will and dreads having to actually 'act' or stand up for himself.