How could she have supposed that she would be able to fulfill these promises? How could she have furnished strength that would be commensurate with the magnitude of the work?
John, “a greater” than whom, according to the judgment of the Savior Himself, “there hath not risen”(Matthew 11:11), did not consider himself worthy even to touch His shoes, and that, when the Lord was leading a life of poverty.
The All-Blameless Virgin was bold enough to carry in her womb the Word Himself, the very Hypostasis of God.
“Who am I, and what is the house of my father?” (2 Kings 7:18). “Even in me, O Lord, shalt Thou save Israel?” (cf. Judges 6:36). Such things are to be heard from righteous men who were called to perform deeds accomplished by many persons and at many times.
But the Blessed Virgin was induced to undertake something unwonted and in no way congruent with human nature, something surpassing all rational understanding—for what else was she doing than elevating the earth to Heaven and through herself changing and transforming all things?—; and she was not shaken in her mind, nor did she perceive her soul to be inferior to this task.
But, just as we are not at all bothered if someone tells us that light is going to strike our eyes, and it is not strange for someone to state that when the sun rises it brings day, so also the Virgin, on learning that she would be capable of conceiving and bearing God Himself, Who is not contained in any place, was not at all surprised.
And she did not leave the words addressed to her unexamined, nor did she experience any light-mindedness, nor was she carried away by the great loftiness of the Angelic laudation, but she restrained herself and focused her attention on the salutation; she inquired into the manner of her conceiving and sought to learn about other matters related to this.
She did not go on to ask whether she was adequate and suited to the great magnitude of this ministry, or whether she had properly purified her body and her soul; rather, concerning what pertained to nature, she was puzzled, whereas she passed over what pertained to the readiness of her soul.
She requested an explanation of the former from Gabriel, but the latter she knew from herself. She had confidence and boldness before God from within, as John says, since her heart was an advocate for her (cf. 1 John 3:21).
Nicholas Cabasilas (1319/1323–after 1391): On the Occasion of the Feast of the Annunciation, 5, Translated from the Greek text in “Homélies Mariales Byzantines (II),” ed. M. Jugie, in Patrologia Orientalis, Vol. XIX, pp. 484-495@ Old Calendar Orthodox Church of Greece.