From a homily in praise of the Virgin Mother by Saint Bernard, abbot
Prepared by the Most High, prefigured by the patriarchs
It was fitting that the Virgin should give birth only to God; and it was also fitting that God should be born only of the Virgin. Accordingly, the Creator of mankind, in order that he might become a man by being born a human being, had to seek out from among all mankind and designate as his mother a woman he knew would be worthy of him and pleasing to him. And so he chose a sinless virgin, that he might be born sinless and free of all stain. He chose a humble virgin, from whom he might come forth meek and humble of heart, to display a most necessary and salutary model of these virtues for all mankind. Thus he allowed a virgin to conceive, in whom he had earlier inspired a vow of virginity, and required of her the merit of humility.
Otherwise how could the angel afterward pronounce her full of grace, if she had the slightest good quality which did not come from grace? Thus she, who was to conceive and bring forth the holy of holies, must be sanctified physically and so she received the gift of virginity; that she might be sanctified spiritually, she received the gift of humility.
The Virgin then, adorned like a queen with the jewels of virtue, shone with the glory of body and soul; and seen on high as radiantly beautiful, she so attracted the inhabitants of heaven that she moved the heart of the King with desire for her and brought down from above the heavenly message. Scripture says: The angel was sent to a virgin. For she was truly virgin in body, virgin in mind, a virgin by her special calling, sanctified, as the Apostle reminds us, in both mind and body. This came about by no unforeseen or accidental occurrence; she was chosen from eternity, foreknown and prepared by the Most High for himself, guarded by the angels, prefigured by the patriarchs, and promised by the prophets.