Catechism of the Catholic Church §865 — excerpt
The Church is ultimately one, holy, catholic, and apostolic in her deepest and ultimate identity, because it is in her that "the Kingdom of heaven," the "Reign of God," already exists and will be fulfilled at the end of time.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.