Lk 24:47 “And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.”

In the generation that Jesus ministered to, a Jew had to change one's mind about who the Messiah is in order to be saved. They as a nation they rejected their Messiah and were the perverse generation Peter mentions in Acts 2. Here we see Repentance is used as a synonym for belief and faith, for salvation. Peter told the Jews in Acts 2 to repent because their leaders led the people to reject Jesus by calling him demon possessed, so they had to repent of their rejection to believe he was their Messiah, they had to change their mind on him. Acts 2:38 Then Peter said unto them, “Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins.” Repentance was used for believing unto for salvation, and “they were baptized” showing they now believed, by an action, baptism.

This declaration to repentance is repeated, "Repent ye therefore, and be converted, that your sins may be blotted out, when the times of refreshing shall come from the presence of the Lord" (Acts 3:19).

Repentance is a necessary element for those who are both unsaved and saved.

Paul did teach repentance -Acts17:30 “And the times of this ignorance God winked at; but now commands all men everywhere to repent.” God commands ALL, not suggests. Peter reiterates the same but gives us the Lords perspective… “The Lord is not slack concerning His promise, as some count slackness, but is longsuffering toward us, not willing that any should perish but that all should come to repentance.” (2 Peter 3:9).

Does this mean we must sorrow over sin first, no, but it means we changed our mind and our direction, we now follow the Lord. Paul preached in Acts 20:20-21: “how I kept back nothing that was helpful, but proclaimed it to you, and taught you publicly and from house to house, testifying to Jews, and also to Greeks, repentance toward God and faith toward our Lord Jesus Christ.

Act 26:19-20  "Therefore, King Agrippa, I was not disobedient to the heavenly vision, but declared first to those in Damascus and in Jerusalem, and throughout all the region of Judea, and then to the Gentiles, that they should repent, turn to God, and do works befitting repentance.
Paul spoke to Jews and gentiles “that they should repent, turn to God, and do works befitting repentance.”

Paul preached repentance. See 2 Cor. 7:2-12; Eph 4:17-24; 2 Tim 2:19-21; Titus 2:11-15).

Rom. 2:4 “Or do you despise the riches of His goodness, forbearance, and longsuffering, not knowing that the goodness of God leads you to repentance?” This verse is heard more than any other on repentance, this goodness is his grace and mercy, for the grace of God has appeared to all men. Gods withholding his judgment brings you to that place of decision.

Paul writes to the church 2 Cor. 12:21: “lest, when I come again, my God will humble me among you, and I shall mourn for many who have sinned before and have not repented of the uncleanness, fornication, and lewdness which they have practiced.” Here Paul wants the believers behavior changed.

Paul also spoke of repentance on behavior to the believers in the church

2 Cor 7:8-10 “For even if I made you sorry with my letter, I do not regret it; though I did regret it. For I perceive that the same epistle made you sorry, though only for a while. Now I rejoice, not that you were made sorry, but that your sorrow led to repentance. For you were made sorry in a godly manner, that you might suffer loss from us in nothing. For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death.” Paul is speaking of a sorrow of doing wrong and sin after one is saved that will change their direction. (of course to do this one has to believe something is wrong.)

Heb 6:1 “Therefore, leaving the discussion of the elementary principles of Christ, let us go on to perfection, not laying again the foundation of repentance from dead works and of faith toward God”

Repentance of not doing, good deeds, or religious works without faith is a basic beginning of those who believe.

It is not necessary to see the word repentance in Scripture to know what is meant by the principle, we see it in responding in an action in numerous examples. Paul writes Col 3:8-10: “But now you yourselves are to put off all these: anger, wrath, malice, blasphemy, filthy language out of your mouth.”

There is a teaching being popularized that repentance has nothing to do with a believer’s life it only is the Old Testament or inter-testamental period.

Here Jesus is speaking to the churches in Asia to repent – but not just of belief, but their actions

Rev. 2:5: "Remember therefore from where you have fallen; repent and do the first works, or else I will come to you quickly and remove your lampstand from its place-- unless you repent.

Rev. 2:16 “Repent; or else I will come unto thee quickly, and will fight against them with the sword of my mouth.”

Rev. 2:21 Pergamos – “And I gave her space to repent of her fornication; and she repented not.”

Rev. 2:22 “Behold, I will cast her into a bed, and them that commit adultery with her into great tribulation, except they repent of their deeds.

Rev. 3:19 “As many as I love, I rebuke and chasten: be zealous therefore, and repent.”