The Lexham Bible Dictionary defines repentance as a change of attitude and action from sin toward obedience to God. When those who heard Peter's sermon at Pentecost just after the Holy Spirit's arrival in tounges of fire, they said, "Brothers, what shall we do?” 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. Peter's reply shows that repentance is here used as a synonym of faith. That's because repentance and faith go together. You can't have saving faith without repentance.