For the ancient Celts, Samhain is the most important of the 4 fire festivals.
Located halfway between the autumn equinox and the winter solstice, it is one of the neighborhood festivals.
For the ancient Celts, Samhain marked the end of the harvest, the first frosts, and they were called to devote their energies to preparations for the coming Winter.
This Time also heralded the day when their ancestors would visit them, crossing the veil with all manner of creatures good and bad that moved freely in the mortal world on the night of Samhain.
Since fairies were often hostile, the Celts disguised themselves as animals or frightening creatures in order to prevent the fairies from kidnapping them.
Christian Influence:
After a first attempt by Pope Boniface to move the Day of the Dead to May 13 without success, it was in the 9th century that Pope Gregory decided to move the day of saints and martyrs to the day of the Day of the Dead.
In the case of Samhain rather than denying the festival of the dead, the Church declared November 1st to be All Saints' Day, the feast of All Saints. Later, November 2nd was All Souls' Day in an attempt to supplant the rituals of the pagans.
Over time, during these family gatherings in Ireland, the night before November 1st, called among other things Hallowe'en, All Saints' Eve, or Hallowmas, ended up concentrating all the ancient pagan traditions.
Festival of Light
Samhain is a festival of light, since the middle ages, in Wales and the Scottish Highlands, young children and servants, go to the village bonfire, light torches and run through the fields to the farms to light up all the properties, all in order to start the festival and scare away the evil fairies or witches.
Torches were often carved out of turnips (before they were made into pumpkins). And these Lanterns are a reference to a Christian legend of Jack O Lanterns.
"A blacksmith named Old Jack: a man so wicked that neither heaven nor hell would have him. With nowhere to go but purgatory, he had to travel the roads on Halloween night, with nothing but a turnip lantern to light his way."
The notion of light was therefore to scare away evil spirits, but also to accompany the ancestors to cross the veil and guide their path to the homes. Candles were generally left on the windows facing West.