Catechism of the Catholic Church §2532 — excerpt
Purification of the heart demands prayer, the practice of chastity, purity of intention and of vision.
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.