From the Anglican Breviary (An Anglican liturgical book borrowed largely from a much earlier Roman Catholic one. It contains readings, meditations, prayers, hymns, and Psalms to be used at daily offices.):

“Now it must be understood that the word Angel is the name of an office rather than the designation of the nature of these beings. For the holy ones of heaven are always spirits, but they are not always accurately called Angels, which is, being interpreted, Messengers, for they are Angels only when they are sent as Messengers. Hence also it is said by the Psalmist : He maketh his Angels spirits, and his Ministers : as to indicate that he has made them spirits, and that of these spirits he sometimes maketh some to minister in the office of messenger. They that go on a lesser ambassage are called Angels, that is Messengers. They that go on a great ambassage are called Archangels, that is Chief Messengers. Hence it is that unto the Virgin Mary was sent no common Angel, but the Archangel Gabriel. […] The individual names also are so given as to signify the kind of ministry wherein each is powerful. Michael is by interpretation : Who is like unto God? Gabriel : The Strength of God. Raphael : The Medicine of God.”

Michael is reported by St. John in the Revelation to have led the angelic host that defeated the rebellious “dragon” (Satan) and his minions and then expelled them from heaven. Thus Michael is often depicted in art with a drawn sword.