Christ rebuked the murmurings of the men and told the Leaders parables to demonstrate God's concern and joy at the repentance of a sinner, one of which was The Lost Sheep. This parable shows how great is the love of God. Although all men belong to God, His chief interest is in the individual person. The lost sheep likened to the sinner. The emphasis is on the joy rather than on the sinner's repentance.
Sheep have a habit of getting lost.
Sheep stray because of curiosity, which represents the unthinking wanderer from God, it is the backslider, pertaining to being lost from the Kingdom of Heaven, and is also a representative of mankind gone astray. The lost sheep has departed from God, and is exposed to certain ruin if not brought back to Him. The sheep that was lost, knew it was lost, yet not desirous to return. The ninety-nine sheep represent those safe in The Kingdom who have been justified. Because of limited faculties the lost sheep cannot find his way back to the rest of the flock.