While his dad is celebrating the gift of his restored family, the older brother still sees trash. In his complaint filed with his father, he names his brother's sins as bluntly as he can, trying to convince his dad that the younger brother is a worthless aggregation of landfill trash.
But the dad isn't listening. He points to the value of both of his sons -- the one who has been found, and the one who was never lost. Both are treasures.
Then he invites his son to the party.
While the bulk of Jesus' story focuses on the younger son, the point may have more to do with the older one. The original audience for this parable isn't a nameless group of people gathered on a hillside. Luke tells us exactly to whom these words were addressed: Pharisees and legal experts -- older brothers -- who are grumbling about Jesus welcoming tax collectors and sinners -- younger brothers.
Jesus tells this story not only so sinners can know their value in the eyes of God, but also to call those who have been redeemed to become redeemers themselves.