Excerpt from a Sermon by St. Ambrose of Milan
The mysteries of God are unsearchable, as is especially declared in the prophetical words: What man is he that can know the counsel of God? or who can think what the will of the Lord is?
Nevertheless, some things have been revealed to us. And hence we may gather, from the words and works of our Lord and Saviour, that there was a special purpose of God in the fact that she who was chosen to bring forth the Lord was espoused to a man.
Why did not the power of the Highest overshadow her before she was so espoused? Perhaps it was lest any might blasphemously say that the Holy One was conceived in fornication.
And the Angel came in unto her. Let us learn from this Virgin how to bear ourselves: let us learn by her devout utterance; above all let us learn by the holy mystery to be timid, to avoid the advances of men, and to shrink from men's addresses. Would that our women would learn from the example of modesty here set before us. She upon whom the stare of men had never been fixed was alone in her chamber, and was found only by an Angel. There was neither companion nor witness there, that what passed might not be debased in gossip; and the Angel saluted her.
The message of God to the Virgin was a mystery so great that it must needs not be uttered by the mouth of man, but only by an Angel. For the first time on earth the words are spoken: The Holy Ghost shall come upon thee. The holy maiden heareth, and believeth.
At length she saith: Behold the handmaiden of the Lord; be it unto me according to thy word. Here is an example of lowliness, here is a pattern of true devotion. At the very moment she is chosen to be the Mother of the Lord she declareth herself to be his handmaid. The knowledge that she was chosen to this high vocation wrought in Mary only an act of humility.