In Luke 15 verse 2 it says that religious leaders reproached Jesus for dealing with sinful people such as harlots and corrupt tax officials:
This Man receives sinners and eats with them. In response, Jesus tells three parables. These three parables in Luke 15 are all about something that was lost and was found.
In the Old Testament, the prophet Ezekiel had prophesied that God - the Shepherd of Israel - Himself would search for His wandering and lost sheep because the unfaithful shepherds failed.
Ezekiel 34.
In Matthew 15 verse 24 Jesus says:
"I was sent only to the lost sheep of the house of Israel".
The younger son who, in the parable of the two sons, left his father’s house to go his own way modelled for one such ‘lost sheep’.
When he returned to his father there was forgiveness and joy. So there is joy in heaven over every sinful man who returns to God.
The eldest son in the parable resembles the religious leaders who accused Jesus of being a friend of sinners.
He was righteous in his own eyes. He despised his brother and showed no love for him.
He was not happy with his return.
Likewise, the spiritual leaders lacked love for the people
'that knew not the law’.
John 7 verse 49.
Unless the eldest son repented of his unloving and haughty attitude, he would be the true ‘lost son’.
This parable could give the impression that God readily forgives the man who comes to Him and pays no attention to the sin he committed.
However, God is merciful, but He is also just.
Sin must be punished.
The way back to God is open only because Jesus bore the penalty in our place.
John 3 verse 16:
For God so loved the world, that He gave His only Son, that whosoever believes in Him should not perish, but have eternal life.
Jesus says in John 14 verse 6:
"I am the way, the Truth, and the Life. No one comes to the Father except through Me".
Jesus mission went beyond just seeking the lost in Israel. In John 10 verse 16 He says:
"And I have other sheep that are not of this fold. I must bring them also, and they will listen to my voice. So there will be one flock, one shepherd".
His work of atonement has universal significance.
‘…Jesus would die for the nation, and not for the nation only, but also to gather into one the children of God who are scattered abroad.
John 11 verse 51 and 52.
See Ephesians 2 verse 11 to 22.