Today, many celebrate the Celtic festival of Samhain or Samuin (pronounced sow-an or sow-in)”. The word is derived from Old Irish and means roughly “summer’s end”. The festival celebrates the end of the “lighter half” of the year and beginning of the “darker half”. It is sometimes regarded as the “Celtic New Year”. The ancient Celts believed that the border between this world and the next became thin on Samhain, allowing spirits (both harmless and harmful) to pass through. The family’s ancestors were honoured and invited home while harmful spirits were warded off. It is believed that the need to ward off harmful spirits led to the wearing of costumes and masks to disguise oneself as a harmful spirit. The word Halloween is first attested in the 16th century and represents a Scottish variant of the fuller All-Hallows-Even (“evening”), that is, the night before All Hallows or All Saints Day when the church celebrates the unity of the church, visible and invisible, earthly and heavenly, the church penitent and the church triumphant.
Read more here stephensizer.com/2010/11/the-need-process-and-results-of-renewal-nehemiah-8/