The synoptic gospels all note that John Baptist came preaching calling to the crowd that they should repent for the kingdom of God is approaching. John baptized with water unto repentance. Although the word, “repent” makes a few more appearances in Matthew and Mark after the initial pericopes with John the Baptist, “repentance” disappears.
Asking someone to repent is asking the person to turn from his or her evil ways. Repentance is more complex. Judaism teaches: "The Day of Atonement atones for sins against God, not for sins against man, unless the injured party has been appeased.” The last clause, "unless the injured party has been appeased”, suggests that for at least one crime, murder, there can be no complete repentance, since there is no way to appease the injured party. I suspect that the same is true where high ranking church officials cover-up years of institutional child abuse. Jewish tradition holds that teshuva consists of several stages: The sinner must recognize his sin, feel sincere remorse, undo any damage he has done and pacify the victim of his offense, and resolve never to commit the sin again.
The New Testament does not explain what “repent” and “repentance” mean suggesting that these passages were written for a Jewish audience. It being so much easier to seek forgiveness from God than from your neighbor, it is understandable that the requirements of repentance were relaxed for Gentiles.
Luke stresses more than the others the need for repentance. All three Synoptics have this saying of Jesus: “I did not come to call righteous people but sinners”; only Luke adds “to repentance.” Luke will not let us escape the demand for repentance. Luke tells us that Jesus uses the repentance of Ninevah as a rebuke to the present unrepentant generation and that he even uses the failure of Tyre and Sidon for the same purpose. Jesus invited his audience to reflect on Pilate’s killing of the Galileans and on the death of those on whom the tower in Siloam fell. He said, “Unless you repent you will all perish likewise.”
When there is repentance, there is joy in heaven. The Lucan Jesus in successive parables repeats this statement. Repentance means an end to sinning. When this happens there is joy beyond this earth. Matthew has a parable about a shepherd looking for a lost sheep and his joy in finding it. In Luke’s version of the story, Jesus says “there will be more joy in heaven over one sinner who repents than over ninety nine righteous persons who need no repentance.”
True Repentance is hard to perform. Consequently, Matthew and Mark had to rewrite Luke to make it palatable by reducing its significance. Matthew and Mark also introduced the theology of the cross missing in Luke. These two changes are related.