From the first chapter of Henry Adams' Mont Saint Michel and Chartres:
The Archangel loved heights. Standing on the summit of the tower that crowned his church, wings upspread, sword uplifted, the devil crawling beneath, and the cock, symbol of eternal vigilance, perched on his mailed foot, Saint Michael held a place of his own in heaven and on earth which seems, in the eleventh century, to leave hardly room for the Virgin of the Crypt at Chartres, still less for the Beau Christ of the thirteenth century at Amiens. The Archangel stands for Church and State, and both militant. He is the conqueror of Satan, the mightiest of all created spirits, the nearest to God. His place was where the danger was greatest; therefore you find him here. For the same reason he was, while the pagan danger lasted, the patron saint of France. So the Normans, when they were converted to Christianity, put themselves under his powerful protection. So he stood for centuries on his Mount in Peril of the Sea, watching across the tremor of the immense ocean,--"immensi tremor oceani"--as Louis XI, inspired for once to poetry, inscribed on the collar of the Order of Saint Michael which he created. So soldiers, nobles, and monarchs went on pilgrimage to his shrine; so the common people followed, and still follow, like ourselves.
Today's feast of the Archangels was one of the important days of the sanctoral and secular year in England before the English Reformation, according to this site:
Michaelmas, or the Feast of Michael and All Angels, is celebrated on the 29th of September every year. As it falls near the equinox, the day is associated with the beginning of autumn and the shortening of days; in England, it is one of the “quarter days”.
There are traditionally four “quarter days” in a year (Lady Day (25th March), Midsummer (24th June), Michaelmas (29th September) and Christmas (25th December)). They are spaced three months apart, on religious festivals, usually close to the solstices or equinoxes. They were the four dates on which servants were hired, rents due or leases begun. It used to be said that harvest had to be completed by Michaelmas, almost like the marking of the end of the productive season and the beginning of the new cycle of farming. It was the time at which new servants were hired or land was exchanged and debts were paid. This is how it came to be for Michaelmas to be the time for electing magistrates and also the beginning of legal and university terms. . . .
Traditionally, in the British Isles, a well fattened goose, fed on the stubble from the fields after the harvest, is eaten to protect against financial need in the family for the next year; and as the saying goes:
“Eat a goose on Michaelmas Day,
Want not for money all the year”.
Sometimes the day was also known as “Goose Day” and goose fairs were held. Even now, the famous Nottingham Goose Fair is still held on or around the 3rd of October. Part of the reason goose is eaten is that it was said that when Queen Elizabeth I heard of the defeat of the Armada, she was dining on goose and resolved to eat it on Michaelmas Day. Others followed suit. It could also have developed through the role of Michaelmas Day as the debts were due; tenants requiring a delay in payment may have tried to persuade their landlords with gifts of geese!
As you might expect, things changed:
Through the celebration of the day in this way, the prosperity and wealth of the family is supported for the coming year. The custom of celebrating Michaelmas Day as the last day of harvest was broken when Henry VIII split from the Catholic Church; instead, it is Harvest Festival that is celebrated now.
The Fisheaters website has more details about other customs on Michaelmas.
Saint Michael the Archangel,
defend us in 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 Divine power of God, cast into hell Satan,
and with him all evil spirits
who prowl through the world seeking the ruin of souls. Amen