The liturgy celebrates the feast of these three archangels who are venerated in the tradition of the Church. Michael (Who is like God?) was the archangel who fought against Satan and all his evil angels, defending all the friends of God. He is the protector of all humanity from the snares of the devil. Gabriel (Strength of God) announced to Zachariah the forthcoming birth of John the Baptist, and to Mary, the birth of Jesus. His greeting to the Virgin, “Hail, full of grace,” is one of the most familiar and frequent prayers of the Christian people. Raphael (Medicine of God) is the archangel who took care of Tobias on his journey.
Useful website for resources on angels: http://www.silk.net/RelEd/angels.htm