Now that one believes that Jesus is the son of God, and the bible is His word, he must obey the commandments that are within.  One of those commandments being repentance, or a changing of one's mind and way of life.  One cannot be a child of God by living a worldly life (I John 2:15).  We find repentance in the bible spoken by the apostle Peter in the book of Acts, chapter 2 & verse 38.  "...'Repent, and let each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you shall receive the gift of the Holy Spirit.'"