The governing theme in this parable [the parable of the Two Prodigals] (and all the stories of Luke 15) is that sin is running from God—avoiding, escaping, saying, "I don't need you!"
This is a much more profound concept than "breaking the rules." Why? Flannery O'Connor grasped this when she said of one of her characters, "There was a deep, black, wordless conviction in him that the way to avoid Jesus was to avoid sin." How could that be? Here is a man who knows that the only way to avoid Jesus as Savior is to avoid sin. If I feel I am a good person, I may look to Jesus as Example, or as Helper, or as Strength—but I won't need to utterly rely on him for every breath and obey him unconditionally. If I am a good person, then I have rights—Jesus owes it to me to listen to my prayers, protect me and reward me.
This is clearly the attitude of the elder brother.
Tim Keller, "The two prodigal sons" (Luke 15:1-3,11-32), a sermon by Tim Keller.