Catechism of the Catholic Church §1199 — excerpt
It is in these churches that the Church celebrates public worship to the glory of the Holy Trinity, hears the word of God and sings his praise, lifts up her prayer, and offers the sacrifice of Christ sacramentally present in the midst of the assembly.
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.