Bible verses about repentance are Luke 13:3 - "I tell you, Nay: but, except ye repent, ye shall all likewise perish" and Acts 17:30, "And the times of this ignorance God winked at; but now commandeth all men every where to repent." Repentance is also mentioned in many other books of the Old and New Testaments.
Repentance is an important concept for Christian theology and is linked to the concept of salvation. One story that illustrates repentance comes from the Old Testament. King David wrote praising psalms to God, but at the same time committed adultery with Bathsheba and murdered her husband Uriah. However, God forgave King David because of his repentance, expressed in Psalm 51, "For I acknowledge my transgressions, and my sin is always before me."
Christian faith holds that there are obstacles in the way of a human being's communion with God, and these obstacles are sins. Satan perverted people's souls, as believed by Christians, and so the humans' natural inclination is to be in conflict with God. Repentance is a way to eradicate this obstacle on a person's way to God. Repentance allows the person to turn away from sin and towards obedience to God. For Christians, this is a step on the way to eternal life.