The Catholic Church retains the structures of episcopal leadership and sacramental life that are the gift of Christ to his Church (cf. CCC, nos. 765, 766) and that date back to apostolic times. At the same time, the Catholic Church recognizes that the Holy Spirit uses other churches and ecclesial communities “as means of salvation, whose power derives from the fullness of grace and truth that Christ has entrusted to the Catholic Church” (CCC, no. 819; LG, no. 8). Depending on what and how much of the elements of sanctification and truth (UR, no. 3) these communities have retained, they have a certain though imperfect com¬munion with the Catholic Church. There are also real differences. In some cases “there are very weighty differences not only of a historical, sociological, psychological and cultural character, but especially in the interpretation of revealed truth” (UR, no. 19). (The word church applies to those bodies of Christians who have a valid episcopal leadership or hierarchy, while the phrase ecclesial communities refers to those bodies of Christians that do not have an apostolic hierarchy.)