Do This and You Shall Live

In Luke 10:25-37, Jesus tells the parable of the Good Samaritan. It's a story most of us have heard. A man is beaten and left for dead. Soon thereafter, a priest and a Levite happen by, both ignoring the man's plight; both were highly respected members of society. Then a Samaritan comes along, [Society would have judged him lower than a dog -- because he was Samaritan] not only helping the man, but going out of his way with time and generosity to make sure he has all he needs.

So, why does Jesus tell the story where a Samaritan is the 'good guy'?

Is this story solely about refuting prejudice? Or does Jesus have further motivation?

There's got to be more to the story...what do you think?