From the Episcopal Church Center:
The term “Halloween” is shortened from “All-hallow-even,” as it is the evening before All Hallows’ Day.
Halloween originated with the Celtic tribes who lived in Ireland, Scotland, Wales and Brittany. For the Celts this Festival marked the end of summer and the coming of winter.
For Celts it is a time when the bridge that separates the world of the living and the world of the dead becomes firmer, allowing spirits and ghosts and ghouls to cross over. These spirits or departed souls are honored and asked to grant luck and prosperity.
The 21st century secular popularity of this holiday has caused the Festival of the Dead to be less about honoring the dead and more about the commercial sale of ghoulish masks and frightening frivolity.
The dressing up was to resemble the souls of the dead which the pagans believed walk the land that night, along with the evil spirits, which people wore masks and lit bonfires to scare them away.
However, over the centuries our Christian beliefs have given way to focusing on honoring the dead through worship, prayer remembrances, and community, not only on All Soul’s Day but also the evening before known as All Hallows’ Eve.
In 1979, the Book of Occasional Services was created as a result of a General Convention Resolution. The All Hallows’ Eve service can be found on page 108. The service of the light, found on page 109, may be used prior to the All Hallows’ Eve service.
The photo, from Wikimedia Commons, shows a cemetery outside a Lutheran church in Röke, Sweden on the feast of All Hallows. Flowers and lighted candles are placed by relatives on the graves of their deceased loved ones.