Catechism of the Catholic Church §1164 — excerpt
From the time of the Mosaic law, the People of God have observed fixed feasts, beginning with Passover, to commemorate the astonishing actions of the Savior God, to give him thanks for them, to perpetuate their remembrance, and to teach new generations to conform their conduct to them.
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.