Catechism of the Catholic Church §2100 — excerpt
Outward sacrifice, to be genuine, must be the expression of spiritual sacrifice: "The sacrifice acceptable to God is a broken spirit...." The prophets of the Old Covenant often denounced sacrifices that were not from the heart or not coupled with love of neighbor.
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.