Lumen Gentium Chapter V is entitled “The Universal Call to Holiness in the Church.” In §40, the Fathers of the Council write:
The followers of Christ are called by God, not because of their works, but according to His own purpose and grace. They are justified in the Lord Jesus, because in the baptism of faith they truly become sons of God and sharers in the divine nature. In this way they are really made holy. Then too, by God’s gift, they must hold on to and complete in their lives this holiness they have received. They are warned by the Apostle to live “as becomes saints” [Eph. 5:3], and to put on “as God’s chosen ones, holy and beloved a heart of mercy, kindness, humility, meekness, patience” [Col. 3:12], and to possess the fruit of the Spirit in holiness. Since truly we all offend in many things we all need God’s mercies continually and we all must daily pray: “Forgive us our debts”. [Emphasis and links to Bible added]
We are not Christians because of any merit on our part; we are Christians by the grace of God. Having been saved, we must live “as becomes saints,” as St. Paul says; we must seek to live holy lives, confessing our sins when we fail.