He Left the Ninety-Nine for the One. We are called to Go Seek the One.
Luke 15:4 & Matthew 18: 12
The parable of the lost sheep is actually a picture of God's perfect love for His creation. Jesus told this story not once but twice in the Bible, which reiterates the importance of the message.
When He said it in Matthew 18, He was talking to His disciples, and in Luke 15, He was addressing the Pharisees.