|Church of Monte Sant'Angelo sul Gargano|
And so it seems like an appropriate day to look at the best known prayer to St Michael for aid, traditionally said in the prayers after Low Mass.
For some reason, it is not included in the Compendium to the Catechism, but it is one of those prayers that surely should be!
The origins of the prayer
According to Michael Martin's excellentThesaurus Precum Latinarum:
"This prayer was composed by Pope Leo XIII after he experienced a horrifying vision. On October 13, 1884, while consulting with his cardinals after Mass, Pope Leo XIII paused at the foot of the altar and lapsed into what looked like a coma. After a little while the Pope recovered himself and related the terrifying vision he had of the battle between the Church and Satan. Afterwards, Pope Leo went to his office and composed this now famous prayer to St. Michael the Archangel and assigned it to be recited after Low Mass, a position it occupied until Vatican II..."
You can read more on the story here.
SANCTE Michael Archangele, defende nos in proelio, contra nequitiam et insidias diaboli esto praesidium. Imperet illi Deus, supplices deprecamur: tuque, Princeps militiae caelestis, Satanam aliosque spiritus malignos, qui ad perditionem animarum pervagantur in mundo, divina virtute, in infernum detrude. Amen.
You can hear it read in Latin here.
This is one of those prayers for which there are a number of different translations in use (often in the same Church!). This seems to be the most commonly used one though:
St. Michael the Archangel, defend us in the day of Battle; Be our safeguard against the wickedness and snares of the Devil. May God rebuke Him, we humbly pray, and do Thou, O Prince of the Heavenly Host, by the power of God, cast into Hell, Satan and all the other evil spirits, who prowl through the world, seeking the ruin of souls. Amen.
Looking at the Latin
SANCTE (holy/saint) Michael Archangele (Archangel), defende (defend) nos (us) in (in) proelio (battle), contra (against) nequitiam (badness/worthlessness) et (and) insidias (ambushes/traps/plots) diaboli (of the devil) esto (be - future imperative) praesidium (help/protection/support)). Imperet (may he [God] command/enjoin/bid) illi (him) Deus (God), supplices (beseeching/begging/humbly) deprecamur (we ask/beg/pray): tuque (and you), Princeps (prince) militiae (of the soldiers) caelestis (heavenly), Satanam (Satan) aliosque (and other) spiritus (spirits) malignos (evil), qui (who) ad (to) perditionem (the ruin) animarum (of souls) pervagantur (they have wandered/robed about/overrun) in mundo (in the world), divina (by God's) virtute (power/strength), in infernum (into hell) detrude (thrust down). Amen.