Catechism of the Catholic Church §2190 — excerpt
The sabbath, which represented the completion of the first creation, has been replaced by Sunday which recalls the new creation inaugurated by the Resurrection of Christ.
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.