Repentance is a condition for salvation.
In those days John the Baptist came preaching in the wilderness of Judea, "Repent, for the kingdom of heaven is at hand." (Mat 3:1-2)Repentance is commanded of all men.
Now after John was arrested, Jesus came into Galilee, proclaiming the gospel of God, and saying, "The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel." (Mar 1:14-15)
And Peter said to them, "Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit. (Act 2:38)
Repent therefore, and turn again, that your sins may be blotted out, that times of refreshing may come from the presence of the Lord, and that he may send the Christ appointed for you, Jesus, whom heaven must receive until the time for restoring all the things about which God spoke by the mouth of his holy prophets long ago. Moses said, 'The Lord God will raise up for you a prophet like me from your brothers. You shall listen to him in whatever he tells you. And it shall be that every soul who does not listen to that prophet shall be destroyed from the people.' (Act 3:19-23)
There were some present at that very time who told him about the Galileans whose blood Pilate had mingled with their sacrifices. And he answered them, "Do you think that these Galileans were worse sinners than all the other Galileans, because they suffered in this way? No, I tell you; but unless you repent, you will all likewise perish. Or those eighteen on whom the tower in Siloam fell and killed them: do you think that they were worse offenders than all the others who lived in Jerusalem? No, I tell you; but unless you repent, you will all likewise perish." (Luk 13:1-5)Repentance is a work of God and man together.
Being then God's offspring, we ought not to think that the divine being is like gold or silver or stone, an image formed by the art and imagination of man. The times of ignorance God overlooked, but now he commands all people everywhere to repent, because he has fixed a day on which he will judge the world in righteousness by a man whom he has appointed; and of this he has given assurance to all by raising him from the dead." Now when they heard of the resurrection of the dead, some mocked. But others said, "We will hear you again about this." (Act 17:29-32)
At midday, O king, I saw on the way a light from heaven, brighter than the sun, that shone around me and those who journeyed with me. And when we had all fallen to the ground, I heard a voice saying to me in the Hebrew language, 'Saul, Saul, why are you persecuting me? It is hard for you to kick against the goads.' And I said, 'Who are you, Lord?' And the Lord said, 'I am Jesus whom you are persecuting. But rise and stand upon your feet, for I have appeared to you for this purpose, to appoint you as a servant and witness to the things in which you have seen me and to those in which I will appear to you, delivering you from your people and from the Gentiles--to whom I am sending you to open their eyes, so that they may turn from darkness to light and from the power of Satan to God, that they may receive forgiveness of sins and a place among those who are sanctified by faith in me.' "Therefore, O King Agrippa, I was not disobedient to the heavenly vision, but declared first to those in Damascus, then in Jerusalem and throughout all the region of Judea, and also to the Gentiles, that they should repent and turn to God, performing deeds in keeping with their repentance. (Act 26:13-20)Repentance is from sin.
Repent, therefore, of this wickedness of yours, and pray to the Lord that, if possible, the intent of your heart may be forgiven you. (Act 8:22)Repentance is from self-sufficiency.
Pay attention to yourselves! If your brother sins, rebuke him, and if he repents, forgive him, and if he sins against you seven times in the day, and turns to you seven times, saying, 'I repent,' you must forgive him." (Luk 17:3-4)
"And to the angel of the church in Sardis write: 'The words of him who has the seven spirits of God and the seven stars. "'I know your works. You have the reputation of being alive, but you are dead. Wake up, and strengthen what remains and is about to die, for I have not found your works complete in the sight of my God. Remember, then, what you received and heard. Keep it, and repent. If you will not wake up, I will come like a thief, and you will not know at what hour I will come against you. (Rev 3:1-3)Repentance is from that which would keep us from turning to Christ.
"'I know your works: you are neither cold nor hot. Would that you were either cold or hot! So, because you are lukewarm, and neither hot nor cold, I will spit you out of my mouth. For you say, I am rich, I have prospered, and I need nothing, not realizing that you are wretched, pitiable, poor, blind, and naked. I counsel you to buy from me gold refined by fire, so that you may be rich, and white garments so that you may clothe yourself and the shame of your nakedness may not be seen, and salve to anoint your eyes, so that you may see. Those whom I love, I reprove and discipline, so be zealous and repent. (Rev 3:15-19)
Being then God's offspring, we ought not to think that the divine being is like gold or silver or stone, an image formed by the art and imagination of man. The times of ignorance God overlooked, but now he commands all people everywhere to repent, because he has fixed a day on which he will judge the world in righteousness by a man whom he has appointed; and of this he has given assurance to all by raising him from the dead." Now when they heard of the resurrection of the dead, some mocked. But others said, "We will hear you again about this." (Act 17:29-32)Repentance is a way of life for the Christian.
Pay attention to yourselves! If your brother sins, rebuke him, and if he repents, forgive him, and if he sins against you seven times in the day, and turns to you seven times, saying, 'I repent,' you must forgive him." (Luk 17:3-4)Unrepentance is a mark of the unregenerate.
Then he began to denounce the cities where most of his mighty works had been done, because they did not repent. "Woe to you, Chorazin! Woe to you, Bethsaida! For if the mighty works done in you had been done in Tyre and Sidon, they would have repented long ago in sackcloth and ashes. But I tell you, it will be more bearable on the day of judgment for Tyre and Sidon than for you. And you, Capernaum, will you be exalted to heaven? You will be brought down to Hades. For if the mighty works done in you had been done in Sodom, it would have remained until this day. But I tell you that it will be more tolerable on the day of judgment for the land of Sodom than for you." (Mat 11:20-24)
The rest of mankind, who were not killed by these plagues, did not repent of the works of their hands nor give up worshiping demons and idols of gold and silver and bronze and stone and wood, which cannot see or hear or walk, nor did they repent of their murders or their sorceries or their sexual immorality or their thefts. (Rev 9:20-21)
The fourth angel poured out his bowl on the sun, and it was allowed to scorch people with fire. They were scorched by the fierce heat, and they cursed the name of God who had power over these plagues. They did not repent and give him glory. The fifth angel poured out his bowl on the throne of the beast, and its kingdom was plunged into darkness. People gnawed their tongues in anguish and cursed the God of heaven for their pain and sores. They did not repent of their deeds. (Rev 16:8-11)