Origins and History of Halloween
The ancient Celts of Ireland and Scotland observed an annual harvest festival on November 1 known as Samhain (pronounced sow'-en or sow'-een), which marked the end of summer and was thought to be the time when the souls of those who had perished during the year journeyed to the "otherworld." During Samhain, it was believed, the dead were able to mingle with the living; ghosts, demons, fairies, and other supernatural beings literally walked the earth. Bonfires were lit and ritual sacrifices were made to honor and appease them.
When the peoples of the British Isles became Christianized during the early Middle Ages these customs and beliefs were transformed, though not abandoned. The Church designated the first and second of November All Saints Day (or All Hallows Day) and All Souls Day respectively -- some say in an effort to eradicate the holiday's pagan trappings -- and October 31 came to be known as All Hallows Even, or Hallowe'en for short.
Among the pre-Christian traditions that survived was the belief that spirits of the dead commingle with the living on the Eve of All Hallows. Related customs arose, or perhaps evolved from existing ones, such as "mumming" and "souling," which entailed the wearing of masks and costumes -- often in imitation of the dead and otherworldly beings -- general mischief making, and knocking on doors to offer prayers in exchange for treats called "soul cakes."
We know little of how these traditions evolved in the intervening centuries, but by the mid-1800s Irish immigrants were bringing the observance of All Hallows Eve to North America, where, combined with homegrown customs, it eventually morphed into the secular, intensely commercialized holiday we celebrate today.I do think I will skip some of the customs, but I wouldn't mind a soul cake. So now we know why.

