St. Thomas Speaks on Mary

and the Hail Mary.  Excerpts:

...it should be known that in ancient times it was an especially great event when an angel appeared to men, so that men might show them reverence, for they deserve the greatest praise. It was written in praise of Abraham that he received angels hospitably and that he showed them reverence. But it was never heard that an angel showed reverence to a man until he saluted the blessed virgin, saying reverently, Hail.

The reason why in antiquity the angel did not reverence man but man the angel is that the angel was greater than man, and this in three respects. First, with respect to dignity, since the angel is of a spiritual nature. Psalm 103,4: “who makes: the angels spirits”. But man is of a corruptible nature, hence Abraham said {Genesis 18:27): “I will speak to my Lord, whereas I am dust and ashes.”

It was not then fitting that a spiritual and incorruptible creature should show reverence to a corruptible creature, namely, man. Second, with respect to familiarity with God. For the angel is a familiar of God, as assisting him. Daniel 7:10: “thousands of thousands ministered to him, and ten thousand times a hundred thousand stood before him”. But man is like an outsider, put at a distance from God through sin. Psalm 54:8: “Lo, I have gone far off, flying away.” Thus it was fitting that man should reverence the angel as one close to and familiar with the king. Third, he was preeminent because of the fullness of the splendor of divine grace: for angels partake most fully of the divine light. Job 25:3: “Is there any numbering of his soldiers, and upon whom shall not his light arise?”

Therefore he always appears with light. But men, although they partake something of the light of grace, it is but little, and with obscurity. Therefore it was not fitting that the angel should show reverence to man until someone should be found in human nature who exceeded the angels in those three respects. And this was the Blessed Virgin. In order to signify that she exceeded him in these three things, the angel wished to show her reverence; hence he said, “Hail.” So the Blessed Virgin exceeded the angels in these three. First, in fullness of grace, which the Blessed Virgin has more than any angel. It was to indicate this that the angel showed her reverence, saying, “full of grace,” as if to say: I will show you reverence because you excel me in the fullness of grace.

He says that the Blessed Virgin is full of grace with respect to three things. First, with respect to soul, which has every fullness of grace. For the grace of God is given for two reasons, namely, in order to act well, and to avoid evil. And with respect to these two the Blessed Virgin had most perfect grace. For more than any other holy person save Christ alone she avoided all sin. For sin is either original, and of this she was cleansed in the womb[1]; or mortal or venial, and of these she was free. Hence the Canticle of Canticles 4:7: “Thou art all fair, O my love, and there is not a spot in thee.” Augustine in “On Nature and Grace” writes: "The holy virgin Mary excepted, if all the holy men and women were here before us and were asked if they were without sin, they would cry out with one voice: 'If we should say we have no sin, we would delude ourselves and the truth is not in us.’"

Except for this holy virgin, I say, of whom for the honor of the Lord, when sin is spoken of, I wish no question at all to be raised...

The Lord is with the Blessed Virgin differently than he is with the angel; he is with her as her son, but with the angel as Lord: the Lord the Holy Spirit, as in the temple, hence she is called the temple of the Lord, the sacred place of the Holy Spirit, “who conceived of the Holy Spirit” (Luke 1:35 ): “the spirit of the Most High shall come upon you.” So it is that the Blessed Virgin is more familiar with God than the angel, because with her is the Lord Father, the Lord Son and the Lord Holy Spirit, that is, the whole trinity is with her. Thus it is sung of her: noble resting place of the whole Trinity. To have said of her, “the Lord is with thee,” is the most noble thing that could be said of her. Rightly then does the angel revere the Blessed Virgin, because she is the mother of the Lord, and therefore mistress herself. The name Mary thus becomes her and in the Syrian tongue it means mistress...

She is celebrated throughout Christian history, in order to rightly celebrate her Son. She who is Theotokos, God-Bearer, by definition of the ecumenical Council of Ephesus is worthy of honor and praise, most blessed among woman. To paraphrase Elizabeth from Scripture: who are we that the Mother of God has come to us? Who are we that Mary should have been borne from among us, to be mother of the Most High God in his flesh?