Catechism of the Catholic Church §822 — excerpt
Concern for achieving unity "involves the whole Church, faithful and clergy alike." But we must realize "that this holy objective - the reconciliation of all Christians in the unity of the one and only Church of Christ - transcends human powers and gifts."
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: UR 5 · UR 24 # 2