Tax collectors and other notorious sinners often came to listen to Jesus teach.
This made the Pharisees and teachers of religious law complain that he was associating with such despicable people -- even eating with them!
So Jesus used this illustration:
"If you had one hundred sheep, and one of them strayed away and was lost in the wilderness, wouldn't you leave the ninety-nine others to go and search for the lost one until you found it?
And then you would joyfully carry it home on your shoulders.
When you arrived, you would call together your friends and neighbors to rejoice with you because your lost sheep was found.
In the same way, heaven will be happier over one lost sinner who returns to God than over ninety-nine others who are righteous and haven't strayed away!"
"Or suppose a woman has ten valuable silver coins and loses one. Won't she light a lamp and look in every corner of the house and sweep every nook and cranny until she finds it?
And when she finds it, she will call in her friends and neighbors to rejoice with her because she has found her lost coin.
In the same way, there is joy in the presence of God's angels when even one sinner repents."
To illustrate the point further, Jesus told them this story: "A man had two sons.
The younger son told his father, 'I want my share of your estate now, instead of waiting until you die.' So his father agreed to divide his wealth between his sons."
"A few days later this younger son packed all his belongings and took a trip to a distant land, and there he wasted all his money on wild living.
About the time his money ran out, a great famine swept over the land, and he began to starve.
He persuaded a local farmer to hire him to feed his pigs.
The boy became so hungry that even the pods he was feeding the pigs looked good to him. But no one gave him anything."
"When he finally came to his senses, he said to himself, 'At home even the hired men have food enough to spare, and here I am, dying of hunger! "
I will go home to my father and say, "Father, I have sinned against both heaven and you,
and I am no longer worthy of being called your son. Please take me on as a hired man."'
"So he returned home to his father. And while he was still a long distance away, his father saw him coming. Filled with love and compassion, he ran to his son, embraced him, and kissed him.
His son said to him, 'Father, I have sinned against both heaven and you, and I am no longer worthy of being called your son.'"
References for Luke 15:21
"But his father said to the servants, 'Quick! Bring the finest robe in the house and put it on him. Get a ring for his finger, and sandals for his feet.
And kill the calf we have been fattening in the pen. We must celebrate with a feast,
for this son of mine was dead and has now returned to life. He was lost, but now he is found.' So the party began."
"Meanwhile, the older son was in the fields working. When he returned home, he heard music and dancing in the house,
and he asked one of the servants what was going on.
'Your brother is back,' he was told, 'and your father has killed the calf we were fattening and has prepared a great feast. We are celebrating because of his safe return.'"
"The older brother was angry and wouldn't go in. His father came out and begged him,
but he replied, 'All these years I've worked hard for you and never once refused to do a single thing you told me to. And in all that time you never gave me even one young goat for a feast with my friends.
Yet when this son of yours comes back after squandering your money on prostitutes, you celebrate by killing the finest calf we have.'"
"His father said to him, 'Look, dear son, you and I are very close, and everything I have is yours.
We had to celebrate this happy day. For your brother was dead and has come back to life! He was lost, but now he is found!'"