What does Luke 15:20 mean?

The prodigal son returns home. He insulted his father, took his money, and fled to a foreign country where he could live as he pleased. It wasn't until the money was gone and a famine took all his food that he realized his "friends" treated him the same way he did his father (Luke 15:11–16). By returning home, he is completing the final step of repentance. The first was acknowledging that he was wrong and his father was right. The second was recognizing that he needed to go to his father and ask for forgiveness (Luke 15:18–19). The third is acting on that understanding. He did not try to justify his sin or find some way that his father could have prevented it. He understands that the fault is entirely his own, and he needs to pay the price.

His intent is to grovel before his father and beg to be treated like the seasonal laborers in the field. The pay is poor, but it provides more food than feeding pigs (Luke 15:17). He probably intends to walk somberly to his father, bow to the ground, perhaps even kiss his feet in submission. He is dirty from working with pigs and traveling; what he has done to his father is even more noxious. But his father doesn't wait for him to come all the way home. Instead, as soon as he sees him, his father runs to him, already prepared to forgive.

The parable of the prodigal son is one of three parables centered around lost things. The first is about a foolish sheep that wanders off. The shepherd leaves the rest of the flock and searches and finds the sheep. The second parable is about a coin that unwittingly rolls away. A woman sweeps the whole house until she finds it (Luke 15:3–10).

In this parable, a son rebelliously and intentionally leaves his father. Instead of searching, the father lets him go. Without developing God's intention too distinctly, it is true that you can't rescue someone else's hardened heart. As Jesus says elsewhere, "If your brother sins against you, go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother" (Matthew 18:15, emphasis added).

Much has been made about how the father runs out to the son, breaking all kinds of cultural taboos. Respectable men in that culture don't run. They don't restore their son so easily. They wouldn't embrace their son until their son was cleaned up.

In the context of these parables, however, the message is simply that God has great grace for intentional sinners. He will readily forgive them and reconcile with them when the sinner repents. When we deliberately disobey and walk away from God, we need to recognize our sin and ask for forgiveness. Until we come to that realization, we're subject to whatever consequences come from those choices.