Catechism of the Catholic Church §1209 — excerpt
, the communion in the faith and the sacraments received from the apostles, a communion that is both signified and guaranteed by apostolic succession.
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.