Albert Barnes on Luke 15:11

And he said. Jesus, to illustrate still farther the sentiment which he had uttered, and to show that it was proper to rejoice over repenting sinners, proceeds to show it by a most beautiful and instructive parable. We shall see its beauty and propriety by remembering that the design of it was simply to justify his conduct in receiving sinners, and to show that to rejoice over their return was proper. This he shows by the feelings of a father rejoicing over the return of an ungrateful and dissipated son.