Today is the Feast of St Michael and All Angels.
The prayer invoking St Michael was conceived by Pope Leo 13th.
Here is one account (of many) of the background to it.
“After Leo XIII had celebrated a morning Mass, he went to a meeting with the Cardinals. Suddenly he collapsed into unconsciousness. The doctors who came to his aid found no cause for the collapse, although his pulse almost ceased. Suddenly he awoke and was fresh as ever. He reported that he had seen a terrible vision. He was granted to see the devil’s seductiveness and ravaging for the coming ages in all lands. In this distress St. Michael the Archangel appeared and cast Satan with all his demons back into the infernal abyss. Leo XIII thereupon ordered, shortly after 1880, the Common Prayer to St. Michael.”
Pope Leo was so shocked by his vision of the unleashing of evil in the Church and in the world in the 20th Century, he asked all Catholics to pray this prayer after celerbrating the Eucharist. (Vatican 2 ended this practice!)
Christians with a sense of the reality of evil and its power have adopted this prayer in both its long and short form. They follow below:
Prayer to St. Michael, the Archangel
St. Michael, the Archangel, defend us in battle. Be our defense against the wickedness and snares of the devil. May God rebuke him, we humbly pray. a Prince of the heavenly host, by the power of God, thrust into hell Satan and the other evil spirits who prowl about the world for the ruin of souls. Amen.
For Holy Church: Longer Version
O glorious Prince of the Heavenly Host, St. Michael, the Archangel, defend us in the battle and in the fearful warfare that we are waging against the principalities and powers, against the rulers of this world of darkness, against the evil spirits. Come thou, to the assistance of men, whom Almighty God created immortal, making them in His own image and likeness and redeeming them at a great price from the tyranny of Satan. Fight this day the battle of the Lord with thy legions of holy Angels, even as of old, thou didst fight against Lucifer, the leader of the proud spirits and all his rebel Angels, who were powerless to stand against thee.
Neither was their place found anymore in Heaven. And that apostle Angel, transformed into an Angel of darkness who still creeps about the earth to encompass our ruin, was cast headlong into the abyss together with his followers.
But, behold, that first enemy of mankind, and a murderer from the beginning, has regained his confidence. Changing himself into an Angel of light, he goes about with the whole multitude of the wicked spirits to invade the earth and blot out the Name of God and of His Christ, to plunder, to slay, and to consign to eternal damnation the souls that have been destined for a crown of everlasting life. This wicked serpent, like an unclean torrent, pours into men of depraved minds and corrupt hearts the poison of his malice, the spirit of lying, impiety, and blasphemy, and the deadly breath of impurity and every form of vice and iniquity. These crafty enemies of mankind have filled to overflowing with gall and wormwood the Church, which is the Bride of the Lamb without spot. They have laid profane hands upon her most sacred treasures.
Make haste, therefore, O invincible Prince, to help the people of God against the inroads of the lost spirits and grant us the victory.
Exorcism Prayer of Pope Leo XIII
In the Name of Jesus Christ, our God and Lord, strengthened by the intercession of the Immaculate Virgin Mary, Mother of God, of Blessed Michael the Archangel, of the Blessed Apostles Peter and Paul and all the Saints, [and powerful in the holy authority of our ministry (parenthesis omitted by lay persons reciting this prayer)], we confidently undertake to repulse the attacks and deceits of the devil.
PSALM 67: God arises; His enemies are scattered and those who hate Him flee before Him.
As smoke is driven away, so are they driven; as wax melts before the fire, so the wicked perish at the presence of God.
V. Behold the Cross of the Lord, flee bands of enemies.
R. He has conquered, the Lion of the tribe of Juda, the offspring of David.
V. May thy mercy, Lord, descend upon us.
R. As great as our hope in Thee.
The crosses indicate a blessing to be given if a priest recites the Exorcism; if a lay person recites it,
they indicate the Sign of the Cross to be made silently by that person.
We drive you from us, whoever you may be, unclean spirits, all satanic powers, all infernal invaders, all wicked legions, assemblies and sects; in the Name and by the power of Our Lord Jesus Christ, + may you be snatched away and driven from the Church of God and from the souls made to the image and likeness of God and redeemed by the Precious Blood of the Divine Lamb. + Most cunning serpent, you shall no more dare to deceive the human race, persecute the Church, torment God’s elect and sift them as wheat. + The Most High God commands you. + He with Whom, in your great insolence, you still claim to be equal; “He Who wants all men to be saved and to come to the knowledge of the truth” [1 Tim. 2: 4]. God the Father commands you. + God the Son commands you. + God the Holy Ghost commands you. + Christ, God’s Word made flesh, commands you; + He Who to save our race outdone through your envy, “humbled Himself, becoming obedient even unto death” [Phil. 2: 8]; He Who had built His Church on the firm rock and declared that the gates of Hell shall not prevail against Her, because He will dwell with Her “all days even to the end of the world” [St. Mat. 28: 20]. The sacred Sign of the Cross commands you, + as does the power of the mysteries of the Christian Faith. + The glorious Mother of God, the Virgin Mary, commands you; + She who by her humility and from the first moment of her Immaculate Conception, crushed your proud head. The faith of the Holy Apostles Peter and Paul and of the other Apostles commands you. + The blood of the Martyrs and the pious intercession of all the Saints commands you. +
Thus, cursed dragon, and you, diabolical legions, we adjure you by the living God, + by the true God, + by the holy God, + by the God “who so loved the world that He gave His only Son, that every soul believing in Him might not perish but have life everlasting” [St. John 3]; stop deceiving human creatures and pouring out to them the poison of eternal damnation; stop harming the Church and hindering her liberty. Begone, Satan, inventor and master of all deceit, enemy of man’s salvation. Give place to Christ in Whom you have found none of your works; give place to the One, Holy, Catholic and Apostolic Church acquired by Christ at the price of His Blood. Stoop beneath the all-powerful Hand of God; tremble and flee when we invoke the Holy and terrible Name of Jesus, this Name which causes Hell to tremble, this Name to which the Virtues, Powers and Dominations of Heaven are humbly submissive, this Name which the Cherubim and Seraphim praise unceasingly repeating: Holy, Holy. Holy is the Lord, the God of Armies.
V. O Lord, hear my prayer.
R. And let my cry come unto Thee.
V. May the Lord be with thee.
R. And with thy spirit.
Let us pray.
God of Heaven, God of earth, God of Angels, God of Archangels, God of Patriarchs, God of Prophets, God of Apostles, God of Martyrs, God of Confessors, God of Virgins, God Who has power to give life after death and rest after work, because there is no other God than Thee and there can be no other, for Thou art the Creator of all things, visible and invisible, of Whose reign there shall be no end, we humbly prostrate ourselves before Thy glorious Majesty and we beseech Thee to deliver us by Thy power from all the tyranny of the infernal spirits, from their snares, their lies and their furious wickedness; deign, O Lord, to grant us Thy powerful protection and to keep us safe and sound. We beseech Thee through Jesus Christ Our Lord. Amen.
From the snares of the devil, deliver us, O Lord.
That Thy Church may serve Thee in peace and liberty, we beseech Thee to hear us.
That Thou may crush down all enemies of Thy Church, we beseech Thee to hear us.
[Holy water is sprinkled in the place where we may be.]