In his testimony before Festus and Agrippa II in Caesarea, Paul recounts his encounter with Christ on the road to Damascus and speaks specifically of the mission Jesus gave to him in that exchange:
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.’ (Acts 26.16-18)
The goal of Jesus' mission for Paul was forgiveness but where does that forgiveness come from? Christ's words here seem to indicate that forgiveness came as people turned "from darkness to light and from the power of Satan to God" and that people would turn as Paul's ministry opened their eyes. So in "obedience to the heavenly vision" Paul preached repentance (turning) (Acts 26:20) to both Jew and Gentile. Repentance was an important part of the gospel message for Paul, Peter (Acts 2:38) and, most importantly, for Jesus (Luke 13:1-5), but does repentance (and the proof shown in our deeds) save us? What about faith? Aren't we saved by grace through faith (Ephesians 2:8-9)? Which one is it?
Both and Neither
In Acts 20:21, we see Paul's preached both repentance towards God and faith in the Lord Jesus. Both turning from sin and trusting in Christ should exist in the life of a Christian. But neither of them do the saving work. We are saved by grace afforded in the death of Christ as a substitute for our sin. Christ's death saves those who receive him (John 1:12) from the wrath of God.
But now the righteousness of God has been manifested apart from the law, although the Law and the Prophets bear witness to it— the righteousness of God through faith in Jesus Christ for all who believe. For there is no distinction: for all have sinned and fall short of the glory of God, and are justified by his grace as a gift, through the redemption that is in Christ Jesus, whom God put forward as a propitiation by his blood, to be received by faith. This was to show God’s righteousness, because in his divine forbearance he had passed over former sins. It was to show his righteousness at the present time, so that he might be just and the justifier of the one who has faith in Jesus. (Romans 3.21-26)
Salvation happens when God's graciously saves a person (2 Cor. 4:4-6) and then enables them to truly repent (to turn) and to have faith. Repentance (Acts 5:31, Romans 2:4) and faith are not prerequisites for salvation but gracious gifts that flow out of a new birth (John 3:3-6).
Understandably a whole set of questions follow.
"Does repentance mean that I should no longer sin?""Isn't it sort of "hell fire and brimstone" preaching to speak of repentance? Isn't it mean to call people to repentance?"
These questions are addressed in this message which ends with a story from NPR's "This I Believe" revealing that it is far more cruel to give a grieving 12 year-old hope in the Beatles than it is to preach repentance.
For further reference: