From Pope St. John Paul II’s Apostolic Exhortation Reconciliatio et Pænitentia (1984):
But there is another aspect to the mysterium pietatis: The loving kindness of God toward the Christian must be matched by the piety of the Christian toward God. In this second meaning of the word, piety (eusebeia) means precisely the conduct of the Christian who responds to God’s fatherly loving kindness with his own filial Piety.
In this sense too we can say with St. Paul that “great indeed is the mystery of our religion.” In this sense too piety, as a force for conversion and reconciliation, confronts iniquity and sin. In this case too the essential aspects of the mystery of Christ are the object of piety in the sense that the Christian accepts the mystery, contemplates it and draws from it the spiritual strength necessary for living according to the Gospel. Here too one must say that “no one born of God commits sin”; but the expression has an imperative sense: Sustained by the mystery of Christ as by an interior source of spiritual energy, the Christian, being a child of God, is warned not to sin and indeed receives the commandment not to sin but to live in a manner worthy of “the house of God, that is, the church of the living God.”109
109 1 Tm 3:15.
— Reconciliatio et Pænitentia 21