Catechism of the Catholic Church §724 — excerpt
In Mary, the Holy Spirit manifests the Son of the Father, now become the Son of the Virgin. She is the burning bush of the definitive theophany.
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.