What does Luke 5:31 mean?

Jesus is explaining to the Pharisees and scribes why He feasted with a group of cultural outcasts and "sinners." He hasn't come for those who believe themselves sinless. He can't heal proud religious leaders who don't think they need God's forgiveness. He has come for those aware enough to know they are sinners and humble enough to repent—like Peter (Luke 5:8).

Peter may have been present at this feast—the text isn't clear if all Jesus' disciples were—but he doesn't immediately get the point that Jesus has come for everybody. Years after Jesus ascends to heaven and Peter becomes a significant church leader, God will go to great lengths to convince him to visit the home of a godly Gentile (Acts 10). When he visits Syrian Antioch, Peter eats with Gentiles until legalistic Jews from Jerusalem arrive and shame him (Galatians 2:11–14). Peter eventually learns to accept Gentiles (Acts 15) and welcomes them as part of the church (1 Peter 2:10). If Peter takes so long to understand following Jesus means breaking tradition and associating with people with varied social standings, the Pharisees' initial interpretation of Jesus' actions as improper is understandable.

A "physician" is someone who cures physical ailments. For a physician to concentrate on healthy people, ignoring those with ailments, is foolish. It's especially unwise when the sick are plentiful and willing to be healed. As with the paralyzed man (Luke 5:23–24), Jesus is using physical healing as a metaphor for spiritual healing. His words here might be a cultural proverb of that era.

It's important for local churches to embody Jesus' statement. We should expect and welcome "sinners" into our congregations. Hospitals and churches are both meant as places people can come with their problems, seeking comfort and relief. A hospital is of little use without those willing to accept that they are sick.