Bede

Your brother has come, and your father has killed the fattened calf, because he received him safe and sound. Your brother was in the ends of the earth, but from there greater joy comes from those singing a new song to the Lord, for his praise from the ends of the earth (Ps. 47). And for him who was absent, that one was sacrificed to whom it was said: "And may your burnt offering be fat" (Ps. 19).

On the Gospel of Luke ↗

Bonaventure

And since the true preacher is the chief announcer of divine mercy, he therefore adds: And he said to him: Your brother has come, through the humility of penance; Isaiah twenty-one: "If you seek, seek: be converted and come"; and chapter sixty: "Your sons shall come from afar, and your daughters shall rise from your side." And your father has killed the fatted calf, through the refreshment of the Eucharist, according to that passage in John six: "My flesh is truly food, and my blood is truly drink. …

Commentary on Luke, Chapter 15 ↗