Catechism of the Catholic Church §2519 — excerpt
The "pure in heart" are promised that they will see God face to face and be like him. Purity of heart is the precondition of the vision of God.
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.