12 However, a rude awakening is in store for the person who thinks that penance is necessary only for those aspiring to membership in the kingdom of God. He who is already a member of Christ must learn of necessity to keep a rein upon himself. Only so will he be able to drive away the enemy of his soul and keep his baptismal innocence unsullied, or regain God's grace when it is lost by sin.
Source: Paenitentiam Agere (Vatican.va)