Jesus talks about one sheep that goes astray. He says nothing about the ninety nine. These were the Scribes and Pharisees who felt no need for Christ. We have to know our need before the Good Shepherd can bring us into the fold. It is the Spirit’s work of conviction of sin that brings us to Christ. I am afraid there are religious people who call themselves Christian but their life shows no indication of a new spirit living inside them who don’t think they are lost. Jesus came to seek and to save those who are lost. He will take the responsibility to bring us home.
The lost coin story is slightly different. How can a coin be lost? I believe this speaks of being lost from the beginning. I had no choice of being born from sinful parents. David says I was born in sin, yes even conceived in sin. In this second story it is not the Shepherd, but the woman who searches for the coin. To me this represents the Holy Spirit who is constantly searching for the souls of people. Of course repentance is mentioned in both and there is joy in Heaven in both stories when the lost is found.