Essentially, Reformed doctrine believes that the same God whose power justified the Christian believer is also at work in the continued sanctification of that believer. As says, "It is God who is at work in you, both to will and work for His good pleasure"; thus, all who are truly born again are kept by God the Father for Jesus Christ, and can neither totally nor finally fall from the state of grace, but will persevere in their faith to the end, and be eternally saved. While Reformed theologians acknowledge that true believers at times will fall into sin, they maintain that a real believer in Jesus Christ cannot abandon one's own personal faith to the dominion of sin, basing their understanding on key scriptural passages such as Christ's words, "By their fruit you will know them" and "He that endures to the end will be saved." Similarly, a passage in 1 John says, "This is how we know who the children of God are and who the children of the devil are: Anyone who does not do what is right is not a child of God." The person who has truly been made righteous in Jesus Christ did not simply have faith at some point in life, but continues to live in that faith (). This view understands that the security of believers is inseparable from their perseverance in the faith.