Even if you aren't Pagan you have to admit, this is the most fun of all the Holidays!
I thought this essay did a pretty good job explaining things. I don't have time to write one myself right now.
You Call It Hallowe'en... We Call It Samhain
Author: Peg Aloi
Posted: October 28th. 2007
Times Viewed: 154,685
Hallowe'en has its origins in the British Isles. While the modern tradition of trick or treat developed in the U. S., it too is based on folk customs brought to this country with Irish immigrants after 1840. Since ancient times in Ireland, Scotland, and England, October 31st has been celebrated as a feast for the dead, and also the day that marks the new year. Mexico observes a Day of the Dead on this day, as do other world cultures. In Scotland, the Gaelic word "Samhain" (pronounced "SAW-win" or "SAW-vane") means literally "summer's end."
This holiday is also known as All Hallows Eve ("hallow" means "sanctify"); Hallowtide; Hallowmass; Hallows; The Day of the Dead; All Soul's Night; All Saints' Day (both on November 1st).
For early Europeans, this time of the year marked the beginning of the cold, lean months to come; the flocks were brought in from the fields to live in sheds until spring. Some animals were slaughtered, and the meat preserved to provide food for winter. The last gathering of crops was known as "Harvest Home, " celebrated with fairs and festivals.
In addition to its agriculture significance, the ancient Celts also saw Samhain as a very spiritual time. Because October 31 lies exactly between the Autumnal Equinox and the Winter Solstice, it is theorized that ancient peoples, with their reliance on astrology, thought it was a very potent time for magic and communion with spirits. The "veil between the worlds" of the living and the dead was said to be at its thinnest on this day; so the dead were invited to return to feast with their loved ones; welcomed in from the cold, much as the animals were brought inside. Ancient customs range from placing food out for dead ancestors, to performing rituals for communicating with those who had passed over.
Communion with the dead was thought to be the work of witches and sorcerers, although the common folk thought nothing of it. Because the rise of the Church led to growing suspicion of the pagan ways of country dwellers, Samhain also became associated with witches, black cats ("familiars" or animal friends), bats (night creatures), ghosts and other "spooky" things...the stereotype of the old hag riding the broomstick is simply a caricature; fairy tales have exploited this image for centuries.
Divination of the future was also commonly practiced at this magically-potent time; since it was also the Celtic New Year, people focused on their desires for the coming year. Certain traditions, such as bobbing for apples, roasting nuts in the fire, and baking cakes which contained tokens of luck, are actually ancient methods of telling fortunes..