…it is only at the older brother’s expense that the younger brother can be brought back in. Because, as Jesus said, the father had divided his property between them before the younger son had left. Everything had been assigned. The younger brother had gotten his one-third portion and it was completely gone. Now, when the father says to the older brother, “My son, everything I have is yours,” he is telling the literal truth. Every penny that remained of the family estate belongs to the elder brother. Every robe, every ring, every fatted calf is his by right.
Over the years many readers have drawn the superficial conclusions that the restoration of the younger brother involved no atonement, no cost. They point out that the younger son wanted to make restitution but the father wouldn’t let him — his acceptance back into the family was simply free. This, they say, shows that forgiveness and love should always be free and unconditional.
That is an oversimplification…. Mercy and forgiveness must be free and unmerited to the wrongdoer. If the wrongdoer has to do something to merit it, then it isn’t mercy, but forgiveness always comes at a cost to the one granting the forgiveness.
— Tim Keller, The Prodigal God