Catechism of the Catholic Church §771 — excerpt
"The one mediator, Christ, established and ever sustains here on earth his holy Church, the community of faith, hope, and charity, as a visible organization through which he communicates truth and grace to all men."
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.
Also cites: LG 8 # 1 · LG 8 · St. Bernard of Clairvaux, In Cant. Sermo 27:14 PL 183:920D