As to the homily as actually said, here is St. Augustine
by this [Luke 2:35] is signified that Mary also, through whom was performed the mystery of the incarnation, looked with doubt and astonishment at the death of her Lord, seeing the Son of God so humbled as to come down even to death
Mary's perfect sanctity
Some few patristic writers expressed their doubts as to the presence of minor moral defects in Our Blessed Lady. [77] St. Basil, e.g., suggests that Mary yielded to doubt on hearing the words of holy Simeon and on witnessing the crucifixion. [78] St. John Chrysostom is of opinion that Mary would have felt fear and trouble, unless the angel had explained the mystery of the Incarnation to her, and that she showed some vainglory at the marriage feast in Cana and on visiting her Son during His public life together with the brothers of the Lord. [79] St. Cyril of Alexandria [80] speaks of Mary's doubt and discouragement at the foot of the cross. But these Greek writers cannot be said to express an Apostolic tradition, when they express their private and singular opinions.
Scripture and tradition agree in ascribing to Mary the greatest personal sanctity; She is conceived without the stain of original sin; she shows the greatest humility and patience in her daily life (Luke 1:38, 48); she exhibits an heroic patience under the most trying circumstances (Luke 2:7, 35, 48; John 19:25-27). When there is question of sin, Mary must always be excepted. [81] Mary's complete exemption from actual sin is confirmed by the Council of Trent (Session VI, Canon 23): "If any one say that man once justified can during his whole life avoid all sins, even venial ones, as the Church holds that the Blessed Virgin did by special privilege of God, let him be anathema." Theologians assert that Mary was impeccable, not by the essential perfection of her nature, but by a special Divine privilege. Moreover, the Fathers, at least since the fifth century, almost unanimously maintain that the Blessed Virgin never experienced the motions of concupiscence.
St. Thomas, Summa Theologica:
I answer that, In every genus, the nearer a thing is to the principle, the greater the part which it has in the effect of that principle, whence Dionysius says (Coel. Hier. iv) that angels, being nearer to God, have a greater share than men, in the effects of the Divine goodness. Now Christ is the principle of grace, authoritatively as to His Godhead, instrumentally as to His humanity: whence (John 1:17) it is written: “Grace and truth came by Jesus Christ.” But the Blessed Virgin Mary was nearest to Christ in His humanity: because He received His human nature from her. Therefore it was due to her to receive a greater fulness of grace than others.