Catechism of the Catholic Church §744 — excerpt
In the fullness of time the Holy Spirit completes in Mary all the preparations for Christ's coming among the People of God. By the action of the Holy Spirit in her, the Father gives the world Emmanuel "God-with-us" (Mt 1:23).
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.