The teaching of all three of these parables is exactly the same. The imagery varies, but the application is constant. That application may be expressed very simply: "God rejoices at the salvation of a sinner; if, therefore, you are really sons of God, you will rejoice too." In the parable of the Prodigal Son, however, the application is forced home more poignantly than in either of the other two. In that parable alone among the three, the Pharisees could see--in the elder brother--a direct representation of themselves.
The incident of the elder brother, sometimes regarded as a mere detail, really introduces the main point of the parable. Everything else leads up to that. The wonderful description of the joy of the father at the prodigal's home-coming is all intended as a contrast to the churlish jealousy of the brother. The elder brother was as far as possible from sharing in the father's joy. That showed that he was no true son. Though he lived under the father's roof, he had no real inward share in the father's life. So it was with the Pharisees. They lived in the Father's house; they were, as we should say, members of the Church. But when salvation, in the person of Jesus, had at last come to the poor, sinful outcasts of the people, the Pharisees drew aside. God rejoiced when the publicans crowded in to Jesus; but the Pharisees held back. That showed that after all they were not, as they thought, true sons of God. If they had been, they would have shared God's feeling.
It should be noticed that the parable ends with an invitation. The elder brother is not harshly rebuked by the father, but tenderly urged to come in still. Will the invitation be accepted? The question is not answered; and there lies the crowning beauty of the parable. The Pharisees are still given a chance. Will they still share the joy of God at the return of his lost children? They must answer the question for themselves.
And we, too, have the same question to answer. If we are really children of God, then we shall not despise the outcasts and the sinners, but shall rejoice with him at their salvation. The parable is characteristic of the Gospel of Luke. Of course, Luke did not compose it. Nothing in the Gospels bears more indisputably the marks of Jesus' teaching. But from the rich store of Palestinian tradition Luke sought out those things which displayed sympathy for the downtrodden and the sick and the sinful. It was an inestimable service to the Church. Shall we heed the message? God rejoices at the salvation of a sinner. Shall we be sharers in his holy joy?