Reply to Objection 3: As Ambrose says on Lk. 1:11: "We are disturbed, and lose our presence of mind, when we are confronted by the presence of a superior power." And this happens not only in bodily, but also in imaginary vision. Wherefore it is written (Gn. 15:12) that "when the sun was setting, a deep sleep fell upon Abram, and a great and darksome horror seized upon him." But by being thus disturbed man is not harmed to such an extent that therefore he ought to forego the vision of an angel. First because from the very fact that man is raised above himself, in which matter his dignity is concerned, his inferior powers are weakened; and from this results the aforesaid disturbance: thus, also, when the natural heat is drawn within a body, the exterior parts tremble. Secondly, because, as Origen says (Hom. iv in Luc.): "The angel who appeared, knowing hers was a human nature, first sought to remedy the disturbance of mind to which a man is subject." Wherefore both to Zachary and to Mary, as soon as they were disturbed, he said: "Fear not." For this reason, as we read in the life of Anthony, "it is difficult to discern good from evil spirits. For if joy succeed fear, we should know that the help is from the Lord: because security of soul is a sign of present majesty. But if the fear with which we are stricken persevere, it is an enemy that we see."
Moreover it was becoming to virginal modesty that the Virgin should be troubled. Because, as Ambrose says on Lk. 1:20: "It is the part of a virgin to be timid, to fear the advances of men, and to shrink from men's addresses."
But others says that as the Blessed Virgin was accustomed to angelic visions, she was not troubled at seeing this angel, but with wonder at hearing what the angel said to her, for she did not think so highly of herself. Wherefore the evangelist does not say that she was troubled at seeing the angel, but "at his saying."