While Act 1 of the parable showed us how free the father’s forgiveness is, Act 2 gives us insight into its costliness. The younger brother’s restoration was free to him, but it came at enormous cost to the elder brother. The father could not just forgive the younger son, somebody had to pay! The father could not reinstate him except at the expense of the elder brother. There was no other way. But Jesus does not put a true elder brother in the story, one who is willing to pay any cost to seek and save that which is lost. It is heartbreaking. The younger son gets a Pharisee for a brother instead.
But we do not.
– Tim Keller, Prodigal God, copyright 2008, page 83-84