What does Luke 15:10 mean?

Jesus finishes the second of three parables about lost things. Pharisees and their lawyers—scribes—are grumbling at Jesus. He has a warm relationship with those who abuse fellow Jews or have abandoned proper God-worship. The parable of the lost sheep addresses sinners who wandered away from God because of their foolishness (Luke 15:1–7).

This parable, the parable of the lost coin, speaks about those who wander off without recognizing it. A coin is unthinking. It can fall and roll away into a dark corner without conscious intent. But the woman who owns it values it, even though it is not worth a massive amount: just a day's wages. She lights a lamp and sweeps the whole house until she finds it. When she does, she invites her friends to celebrate with her (Luke 15:8–9). In the same way, God desires a relationship with those who don't know they've abandoned Him. When such a sinner repents, heaven, itself, rejoices.

The image of the celebration is suspenseful. In the parable of the lost sheep, the celebration was in heaven (Luke 15:7). Now, it is "before the angels." In the upcoming parable of the prodigal son, we learn that it is God, Himself, who rejoices when the sinner returns to Him (Luke 15:21–24).