"Secondly, that she might be a more certain witness of this mystery, being instructed therein by God.
"Thirdly, that she might offer to God the free gift of her obedience: which she proved herself right ready to do, saying: "Behold the handmaid of the Lord."
"Fourthly, in order to show that there is a certain spiritual wedlock between the Son of God and human nature. Wherefore in the Annunciation the Virgin's consent was besought in lieu of that of the entire human nature."
~St. Thomas Aquinas: Summa Theologica, III, Q. 30, A. 1.
Annunciation, by Federico Fiori Barocci. Oil on canvas,
1592-96; Santa Maria degli Angeli, Perugia.