When she had seen him, she was agitated Luke does not say that she was agitated by the presence of the angel, but by his address. Why then does he also mention his presence? [1] The reason, I think, is this. Perceiving in the angel something of heavenly glory, she was seized with sudden dread arising out of reverence for God. She was agitated, because she felt that she had received a salutation, not from a mortal man, but from an angel of God. But Luke does not say that she was so agitated as to have lost recollection. On the contrary, he mentions an indication of an attentive and composed mind; for he afterwards adds, and was considering what that salutation would be: that is, what was its object, and what was its meaning. It instantly occurred to her that the angel had not been sent for a trifling purpose. This example reminds us, first, that we ought not to be careless observers of the works of God; and, secondly, that our consideration of them ought to be regulated by fear and reverence.

Footnotes

1 - "Cur ergo aspectus etiam meminit?" Calvin's allusion is brought out more clearly in his own vernacular. "Pourquoy donc dit-il, Quand elle l'eut veu?" -- "Why then does he say, When she had seen him?"

Troubled at his saying - Disturbed or perplexed at what he said. It was so unexpected, so sudden, so extraordinary, and was so high an honor, that she was filled with anxious thoughts, and did not know what to make of it.
Cast in her mind - Thought, or revolved in her mind.
What manner of salutation - What this salutation could mean.

She was troubled at his saying - The glorious appearance of the heavenly messenger filled her with amazement; and she was puzzled to find out the purport of his speech.

And when she saw [him], she was (b) troubled at his saying, and cast in her mind what manner of salutation this should be.
(b) Moved at the strangeness of the matter.

And when she saw him,.... The Persic version renders it, "when Mary saw the angel"; which expresses the true sense of the words, The Vulgate Latin reads, "when she heard"; i.e. the salutation:
she was troubled at his saying; at his speaking to her; she was surprised at the sight of him, and more at what he said to her,
and cast in her mind, or thought and reasoned within herself,
what manner of salutation this should be; for it was not usual with the Jews for a man to use any salutation to a woman; with them it was not lawful to be done in any shape or form; not by a messenger, nor even by her own husband (u); so that Mary might well be thrown into a concern what should be the meaning of this; and especially, that she should be addressed in such language, and saluted as a peculiar favourite of God, and blessed among women,
(u) T. Bab. Kiddushin, fol. 70. 1, 2. Maimon. Hilch. Issure Biah, c. 21.