Luke 15:3-7

So Jesus told them this parable:  “Which one of you, if he has a hundred sheep and loses one of them, would not leave the ninety-nine in the open pasture and go look for the one that is lost until he finds it?  Then when he has found it, he places it on his shoulders, rejoicing.  Returning home, he calls together his friends and neighbors, telling them, ‘Rejoice with me, because I have found my sheep that was lost.’  I tell you, in the same way there will be more joy in heaven over one sinner who repents than over ninety-nine righteous people who have no need to repent.

It is a selfless thing: the ability to understand and rejoice at the truth of this parable. It is like the story of the prodigal son when he returns home and the other son could not rejoice in his heart about it because he felt slighted. Yet, the son's father immediately rejoiced and brought out a fine robe and the best of the best to celebrate his return. The 99 sheep are sinners too, but are made righteous by the blood of Christ: the Shepherd. The question is, can the hearts of the 99 sheep rejoice at the return of the one? Repentance brings great joy to Jesus!