First, why have a feast of archangels? They are God's servants, always doing His will, and especially to establish special relationships with Man or perform special tasks. St. Michael led the angels in casting Satan from Heaven, and closed the Garden of Eden. St. Raphael assisted Tobias in the Book of Tobit, and the Incarnation was made known by the message of an angel, specifically St. Gabriel.
Prayers to angels dates back to the very earliest parts of the Church, and it's clear that we pray in union with them and the Saints in heaven during the liturgy, as the priest references the choirs of angels during the Preface. Other liturgical prayers to the angels can be found, as well as great private devotion to one's guardian angel (the feast of whom is on October 2).
Why is it "the dedication..."? Apparently, St. Michael the Archangel appeared on a mountain in rural Italy in the late fifth century, and signalled that a church was to be erected on the spot. The writings of the great Fr. Lasance on this interesting story can be found here.
Did you know that the intercession of St. Michael is in the Confiteor of the traditional form, as well as the blessing of incense at the Offertory? The former signifies St. Michael's special place as a messenger of God, behind Our Lady the perfect embodiment of faith, and with St. John the Baptist, the only Prophet to encounter Our Lord incarnate. The latter is in reference to Revelation 8: 3-4, "The angel stood before the altar of the temple, having a golden censer in his hand;"
This is the longer St. Michael Prayer, used during certain exorcism rites. It was composed by Pope Leo XIII, after a series of visions involving spiritual warfare. Satan challenged God, and said he needed 100 years to destroy the world. God allowed great evil to occur during this century (the 20th, of course), and the Holy Father wrote these prayers for the defense of Christians and all others from Hell and great earthly trials.
We should all pray the shorter, more familiar version. It should also be restored after Mass, along with the triple Ave's, the Salve Regina, and the prayer for the conversion of sinners and the liberty of the Church, plus the invocation of the Sacred Heart of Jesus.
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.
Traditionally, kids have just come off a holiday at certain English schools. So may God bless them, and St. Michael watch over them, as they go back to school... and may they kick butt on the rugby pitch!SAINT 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. And do thou, O prince of the heavenly host, by the power of God thrust into hell Satan and all the evil spirits who prowl about the world for the ruin of souls. Amen.