We say that there are nine orders or choirs of Angels, for, by the witness of the holy Word, we know that there be Angels, Archangels, Virtues, Powers, Principalities, Dominions, Thrones, Cherubim, and Seraphim. Nearly every page of the holy Word witnesseth that there be Angels and Archangels. The books of the Prophets, as is well known, do often-times make mention of Cherubim and Seraphim. The Apostle Paul, writing to the Ephesians, counteth up the names of four orders, where he saith: Far above all Principality, and Power, and Virtue, and Dominion. And the same, again, writing to the Colossians, saith: Whether they be Thrones, or Dominions, or Principalities, or Powers. If, then, we add the Thrones to the four orders of which he spoke unto the Ephesians, we have five orders; and when we add unto them the Angels and the Archangels, the Cherubim and the Seraphim, we find that the orders of Angels are beyond all doubt nine.
But we must know that the word Angel is the designation, not of a nature, but of an office. Those holy spirits in the heavenly fatherland are always spirits, but they may in nowise be always called Angels. For they are Angels only when they are sent as Messengers. Hence also it is said by the Psalmist: Who makest spirits thine Angels! as if it were: Of them who are always with him as spirits, he doth sometimes make use as Messengers. They who go on the lesser messages are called Angels: they who go on the greater Archangels. Hence it is that unto the Virgin Mary was sent no common Angel, but the Archangel Gabriel. For the delivery of this, the highest message, it was meet that there should be sent the highest Angel. Their individual names also are so given as to signify the kind of ministry wherein each is powerful. Michael signifieth Who is like unto God? Gabriel, The Strength of God. And Raphael, The Medicine of God.
As often as anything very mighty is to be done, we see that Michael is sent, that by that very thing, and by his name, we may remember that none is able to do as God doeth. Hence that old enemy whose pride hath puffed him up to be fain to be like unto God, even he who said: I will ascend unto heaven, I will exalt my throne above the stars of God. I will be like the Most High, this old enemy, when at the end of the world he is about to perish in the last death, having no strength but his own, is shown unto us a-fighting with Michael the Archangel, even as saith John: There was a war in heaven: Michael and his Angels fought against the dragon; and the dragon fought and his angels. Unto Mary is sent Gabriel, whose name is interpreted The Strength of God, for he came to herald the appearing of him who was content to appear lowly that he might fight down the powers of the air. Raphael, also, as we have said, signifieth The Medicine of God, and it is the name of him who touched as a physician the eyes of Tobias, and cleared away his blindness.
O glorious Archangel St. Michael, Prince of the heavenly host, defend us in battle, and in the struggle which is ours against the principalities and Powers, against the rulers of this world of darkness, against spirits of evil in high places (Eph 6:12). Come to the aid of men, whom God created immortal, made in his own image and likeness, and redeemed at a great price from the tyranny of the devil (Wis 2:23-24, 1 Cor 6:20).
Fight this day the battle of the Lord, together with the holy angels, as already thou hast fought the leader of the proud angels, Lucifer, and his apostate host, who were powerless to resist thee, nor was there place for them any longer in Heaven. But that cruel, that ancient serpent, who is called the devil or Satan, who seduces the whole world, was cast into the abyss with all his angels (Rev 12:7-9).
Behold, this primeval enemy and slayer of man has taken courage, Transformed into an angel of light, he wanders about with all the multitude of wicked spirits, invading the earth in order to blot out the name of God and of his Christ, to seize upon, slay and cast into eternal perdition souls destined for the crown of eternal glory. This wicked dragon pours out, as a most impure flood, the venom of his malice on men of depraved mind and corrupt heart, the spirit of lying, of impiety, of blasphemy, and the pestilent breath of impurity, and of every vice and iniquity.
These most crafty enemies have filled and inebriated with gall and bitterness the Church, the spouse of the Immaculate Lamb, and have laid impious hands on her most sacred possessions (Lam 3:15).
In the Holy Place itself, where has been set up the See of the most holy Peter and the Chair of Truth for the light of the world, they have raised the throne of their abominable impiety, with the iniquitous design that when the Pastor has been struck, the sheep may be scattered.
Arise then, O invincible prince, bring help against the attacks of the lost spirits to the people of God, and bring them the victory.
The Church venerates thee as protector and patron; in thee holy Church glories as her defense against the malicious powers of this world and of hell; to thee has God entrusted the souls of men to be established in heavenly beatitude.
Oh, pray to the God of peace that He may put Satan under our feet, so far conquered that he may no longer be able to hold men in captivity and harm the Church. Offer our prayers in the sight of the Most High, so that they may quickly conciliate the mercies of the Lord; and beating down the dragon, the ancient serpent, who is the devil and Satan, do thou again make him captive in the abyss, that he may no longer seduce the nations.
(Rituale Romanum, 6th ed. post typicam, (Ratisbon: Pustet 1898), 163ff).