Jesus tells the parable of the lost sheep to show that the Kingdom of God is accessible to all, even those who were sinners or strayed from God’s path.
He uses the example of a shepherd (God) who has 100 sheep and one goes missing.
The shepherd leaves the 99 others and searches high and low for the lost sheep.
Jesus stresses that when the shepherd finds the lost sheep he rejoices over it more than the 99 who did not go astray.
This is how God will rejoice when a sinner returns to Him.