I just started reading The Prodigal God: Recovering the Heart of the Christian Faith (Dutton, 2008) by Tim Keller. Here's a great thought on Jesus' intention in telling the parable,
...the original listeners were not melted into tears by this story but rather they were thunderstruck, offended, and infuriated. Jesus' purpose is not to warm our hearts but to shatter our categories. Through this parable Jesus challenges what nearly everyone has ever thought about God, sin, and salvation. His story reveals the destructive self-centeredness of the younger brother, but it also condemns the elder brother's moralistic life in the strongest terms. Jesus is saying that both the irreligious and the religious are spiritually lost, both life-paths are dead ends, and that every thought the human race has had about how to connect to God has been wrong. (pp. 10-11)
And...here's a good sermon on the parable that expands on Keller's point (though admittedly I'm a tad biased).