Q. Where does the Bible teach that we receive forgiveness of sin when we repent?
A. The Greek word for repent means to change our mind about something. After His resurrection Jesus told the disciples that repentance and the forgiveness of sins would be preached in His name to all nations beginning in Jerusalem (Luke 24:47). What he meant was that due to their preaching, people would change their minds about what it takes to be forgiven. Because of His death and resurrection they could now ask in His name and receive forgiveness.
John, who was there, would confirm this later when he wrote;
“If we confess our sins, He is faithful and just and will forgive us our sins and purify us from all unrighteousness” (1 John 1:9)
Therefore the Bible doesn’t teach that we receive forgiveness when we repent. It teaches that we receive forgiveness when we confess.
If you confess with your mouth, “Jesus is Lord” and believe in your heart that God raised Him from the dead, you will be saved (Romans 10:9).