What does Luke 15:9 mean?

Three parables explain why Jesus chooses to interact with "sinners" and "tax collectors." The first, the parable of the lost sheep, illustrates that some are lost because of foolishness. That being the case, it's unlikely they'll be able to find their way home, so Jesus—the Good Shepherd (John 10:11)—goes after them (Luke 15:1–7).

In the parable of the lost coin, Jesus compares a missing silver coin to a person who does not know he has strayed from following God. Such a lost person cannot return on his own. God is represented by a woman who searches her house diligently until she finds the coin (Luke 15:8). When she does, she invites her friends and neighbors to celebrate with her. In the same way, when a sinner turns from his way and repents, heaven will celebrate the restoration.

The value of the coin in this example was about a day's wage. While not a trivial amount, this is also not a catastrophic loss. To men like the ancient Pharisees, a single sinner doesn't seem important enough to make such a fuss over. Certainly not enough for a respected teacher—Jesus—to sully His reputation.

"Friends" and "neighbors" here are both in feminine form as opposed to the masculine found in Luke 15:6. Luke's Gospel is known for including many stories and parables where the protagonist is a woman.