Catechism of the Catholic Church §1111 — excerpt
Christ's work in the liturgy is sacramental: because his mystery of salvation is made present there by the power of his Holy Spirit; because his Body, which is the Church, is like a sacrament (sign and instrument) in which the Holy Spirit dispenses the mystery…
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.