Luke 15:11

And He said, A Certain man had two sons. This parable is the third of the series, and like the two preceding ones, is designed to show the joy which is in heaven over the conversion of a sinner. And so there are three principal persons in the parable, the father and his two sons, the elder careful of his possessions, the younger a spendthrift. The father is God, who created all men, or Christ, who redeemed and regenerated all men with His blood, and who daily regenerates them by baptism. The two sons are understood by universal consent to represent the Jews and the Gentiles. By the elder, who was ever with his father, we may understand the Jews; by the younger the Gentiles, who having worshipped God in the days of Adam and Noah, turned aside to idols and the sins of the flesh: an interpretation which is borne out by the 25th verse, for it was the Jews who murmured because the Gentiles were received into grace and favour by Christ.

But still more in accordance with the purpose of the parable, we may take the two sons to represent the just and the unjust, whether Jews or Gentiles. For the sinners with whom Christ companied, thereby causing the Pharisees to murmur against Him, were clearly Jews and not Gentiles.

The elder son represents the just, i.e. those who were really just, as well as those who, like the Scribes and Pharisees, claimed to be such.

The younger son, the prodigal, is put for open and notorious sinners, such as the publicans and harlots, with whom Christ was wont to associate in order that He might win them from the error of their way. So S. Jerome and most other interpreters explain the parable.