Catechism of the Catholic Church §921 — excerpt
They manifest to everyone the interior aspect of the mystery of the Church, that is, personal intimacy with Christ. Hidden from the eyes of men, the life of the hermit is a silent preaching of the Lord, to whom he has surrendered his life simply because he is everything to him.
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.