Catechism of the Catholic Church §2045 — excerpt
Because they are members of the Body whose Head is Christ, Christians contribute to building up the Church by the constancy of their convictions and their moral lives.
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 39