Some angels are given proper names to denote their special service. Thus, Michael means "Who is like God"; Gabriel is "The Strength of God"; and Raphael is "God's Remedy"
As I watched, thrones were set in place, and an Ancient One took his throne, his clothing was white as snow, and the hair of his head like pure wool; his throne was fiery flames, and its wheels were burning fire. A stream of fire issued and flowed out from his presence. A thousand thousands served him, and ten thousand times ten thousand stood attending him. The court sat in judgment, and the books were opened.
As I watched in the night visions, I saw one like a human being coming with the clouds of heaven. And he came to the Ancient One and was presented before him. To him was given dominion and glory and kingship, that all peoples, nations, and languages should serve him. His dominion is an everlasting dominion that shall not pass away, and his kingship is one that shall never be destroyed.
When Jesus saw Nathanael coming toward him, he said of him, "Here is truly an Israelite in whom there is no deceit!" Nathanael asked him, "Where did you get to know me?" Jesus answered, "I saw you under the fig tree before Philip called you." Nathanael replied, "Rabbi, you are the Son of God! You are the King of Israel!" Jesus answered, "Do you believe because I told you that I saw you under the fig tree? You will see greater things than these." And he said to him, "Very truly I tell you, you will see heaven opened and the angels of God ascending and descending upon the Son of Man."
Excerpt from a homily (PL 76, 1250-1251) of St Gregory the Great: Office of Readings for the Feast.
The word "angel" denotes a function rather than a nature. Those holy spirits of heaven have indeed always been spirits . They can only be called angels when they deliver some message. Moreover, those who deliver messages of lesser importance are called angels; and those who proclaim messages of supreme importance are called archangels. And so it was that not merely an angel but the archangel Gabriel was sent to the Virgin Mary. It was only fitting that the highest angel should come to announce the greatest of all messages.
Some angels are given proper names to denote the service they are empowered to perform. In that holy city, where perfect knowledge flows from the vision of almighty God, those who have no names may easily be known. But personal names are assigned to some, not because they could not be known without them, but rather to denote their ministry when they came among us. Thus, Michael means "Who is like God"; Gabriel is "The Strength of God"; and Raphael is "God's Remedy."
Whenever some act of wondrous power must be performed, Michael is sent, so that his action and his name may make it clear that no one can do what God does by his superior power. So also our ancient foe desired in his pride to be like God, saying: I will ascend into heaven; I will exalt my throne above the stars of heaven; I will be like the Most High. He will be allowed to remain in power until the end of the world when he will be destroyed in the final punishment. Then, he will fight with the archangel Michael, as we are told by John: A battle was fought with Michael the archangel.
So too Gabriel, who is called God's strength, was sent to Mary. He came to announce the One who appeared as a humble man to quell the cosmic powers. Thus God's strength announced the coming of the Lord of the heavenly powers, mighty in battle. Raphael means, as I have said, God's remedy, for when he touched Tobit's eyes in order to cure him, he banished the darkness of his blindness. Thus, since he is to heal, he is rightly called God's remedy.