In this battle against our inclination towards evil, who could be brave and watchful enough to escape every wound of sin? "If the Church has the power to forgive sins, then Baptism cannot be her only means of using the keys of the Kingdom of heaven received from Jesus Christ. The Church must be able to forgive all penitents their offenses, even if they should sin until the last moment of their lives."
Source: Catechism of the Catholic Church (Vatican.va)