Catechism of the Catholic Church §230 — excerpt
Even when he reveals himself, God remains a mystery beyond words: "If you understood him, it would not be God" (St. Augustine, Sermo 52, 6, 16: PL 38, 360 and Sermo 117, 3, 5: PL 38, 663).
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.