Catechism of the Catholic Church §484 — excerpt
The Annunciation to Mary inaugurates "the fullness of time", The time of the fulfilment of God's promises and preparations. Mary was invited to conceive him in whom the "whole fullness of deity" would dwell "bodily".
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.