Catechism of the Catholic Church §1112 — excerpt
The mission of the Holy Spirit in the liturgy of the Church is to prepare the assembly to encounter Christ; to recall and manifest Christ to the faith of the assembly; to make the saving work of Christ present and active by his transforming power;…
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.