Fear not, Mary He bids her lay aside fear. Let us always remember--what arises from the weakness of the flesh--that, whenever the feeblest ray of the Divine glory bursts upon us, we cannot avoid being alarmed. When we become aware, in good earnest, of the presence of God, we cannot think of it apart from its effects. [1] Accordingly, as we are all amenable to his tribunal, fear gives rise to trembling, until God manifests himself as a Father. The holy virgin saw in her own nation such a mass of crimes, that she had good reason for dreading heavier punishments. To remove this fear, the angel declares that he has come to certify and announce an inestimable blessing. The Hebrew idiom, Thou hast found favor, is used by Luke instead of, "God has been merciful to thee:" for a person is said to find favor, not when he has sought it, but when it has been freely offered to him. Instances of this are so well known, that it would be of no use to quote them.

Footnotes

1 - "Neque otiosam imaginari licet." -- "Car nous ne pouvons point apprehender à bon escient la presence de Dieu, sinon avec ses effects."

Fear not, Mary - Do not be alarmed at this appearance of an angel. He only comes to announce to you good tidings. Similar language was addressed by an angel to Joseph. See the notes at Matthew 1:20.
Thou hast found favour with God - Eminent favor or mercy in being selected to be the mother of the Messiah.

And the angel said unto her, Fear not, Mary: for thou hast (c) found favour with God.
(c) So the Hebrews said, saying that those men have found favour who are in favour.

And the angel said unto her, &c. Observing the consternation and confusion she was in,
fear not, Mary; he calls her by her name, signifying that she was well known to him, as the saints are to the ministering angels, who are often sent unto them, encamp about them, and do them many good offices; and bids her not be afraid, he had no ill design upon her, nor brought any ill news to her:
for thou has found favour, or "found grace with God"; and what that particular grace and favour was, is expressed in the following verses.

Fear not. In the angel's message we have, (1) An assurance, Fear not. (2) A promise, Thou shalt bring forth a son. (3) A command, Thou shalt call his name Jesus. (4) A prophecy, He shall be great, the Son of the Highest, sit on David's throne, reign forever.