The moment when God's request to Mary will, by her consent, be fulfilled, is called the fullness of time. This means that time and eternity have touched in a single moment of embrace and will never separate again, either for all time or for all eternity. Let us first consider the great messenger whom God chose, out of His three hierarchies, His nine choirs of angels, to bring this message to Mary, who is about to become the Mother of God. The great messenger's name is Gabriel, and he is one of the seven angels who stand before the throne of God. Three of these seven angels who stand before the throne of God we know the names of.
Every angel is a messenger, because that is what the word angel means.
But Gabriel is the messenger of all messengers, the mouthpiece, the megaphone of God. So completely is this great angel and pure spirit dedicated to the work of being messenger that, when his task is assigned to him, he outfits himself for the purpose, and if his message is one from God to man, he outfits himself as a man, when he arrives to bring his divine greeting or divine news. In the Old Testament, we encounter this great angel Gabriel very especially in the Book of Daniel the prophet, when he comes to tell Daniel how long it will be from his day to the coming of Jesus - and of Jesus' rejection by the Jews. He tells Daniel of the punishment of the Jews which will follow upon their rejection of their King, then the Temple of Jerusalem will be destroyed, never to be rebuilt again unless just before the ultimate consummation of things, at the end of the world. Daniel the prophet speaks of Gabriel as the Man of God.