The name Halloween is a blending of the words All Hallows’ Eve or Even (referring to the evening before All Saints’ Day on November 1). The term hallow means “holy” – you may recall reciting it in the Lord’s Prayer, “Our Father who art in heaven, hallowed be thy name” (Matthew 6:9).
From the early days of the church, saints (more specifically martyrs – the only persons initially recognized as saints) were honored and celebrated. However, with time, the growing number of martyrs (particularly under the persecution of Diocletian, the Roman Emperor from 284-305 AD) made it impossible to assign a separate celebration for each. Thus, various churches made an effort to select a common day to commemorate all the saints….
Many scholars claim that Gregory III chose to commemorate the saints on November 1 in order to combat an ancient pagan Celtic festival called Samhain that was celebrated on the same day. However, Samhain seems to have been a tradition limited to the Northern Celtic people (particularly in Ireland and Scotland), and since these areas were Christianized by this time, it is difficult to substantiate this assertion. Furthermore, it should be noted that the Irish celebrated saints on April 20, “a chronology that contradicts the widely held view” that Rome adopted the November 1 date under Celtic influence. Lastly, if remnants of pagan practices remained only in the remote parts of Christian lands, they were probably not of particular concern to the Christian leadership in Rome. Scholar Francis X. Weiser believes that November 1 was chosen so that the many pilgrims who traveled to Rome for the Feast “could be fed more easily after the harvest than in the spring.”
Samhain (pronounced sow-in) is a name derived from Old Irish that roughly means “summer’s end.” Practically speaking, it was a time to prepare for the harvest, shelter (and slaughter) animals, welcome home soldiers and kings, and generally reorganize communities in preparation for the coming cold weather.
Whatever claims are made about the ancient pagan celebration of Samhain are purely speculative. There were no written records among the northern Celtic people prior to their Christianization in the 5th century. Early Roman sources from the first century BC note the superstitious nature of the Celts and how they would celebrate their festivals with fire and sacrifices (both animal and human), but there is no specific mention of Samhain….
[T]here is no indication that ancient Samhain was ever a festival of the dead or dedicated to some Lord of the Dead.