Read: Luke 15:11-32
It was fitting to celebrate and be glad, for this your brother was dead, and is alive; he was lost, and is found. (Luke 15:32 ESV)
Have you ever lost something dear to you? What happened when you found it? Losing stuff is a big pet peeve of mine so when it does happen I am dearly invested in finding it. I get really excited when I find something I have lost.
Jesus was clear in his famous story about the prodigal son. The Father celebrates lost things. He loves to celebrate lost things. Furthermore, He refuses to allow anything, including self righteous religious people, to get in the way of His welcoming celebration.
Outside of God we are dead. Lostness, life not lived under the saving grace of Jesus, is death. Salvation restores us to God. The Father loves and longs to celebrate that. He even goes so far as to say that celebrating the return of a lost son or daughter is expected. It is fitting.