Halloween's Pagan Origin
"Its name means hallowed or holy evening." - The World Book Encyclopedia, 1952, Vol. 8, pp. 3245-6.
To really understand this "holy evening" you must realize that Halloween, as we know it today, has grown from several different sources. The main source has been traced back to religious ceremonies of the ancient Babylonians. - The New Golden Bough, Sir James Frazer, edited by Dr. T. H. Gaster, p. 468, Mentor Book, 1964; and Funk and Wagnalls Standard Dictionary of Folklore, Mythology, and Legend, 1949, p. 38.
From Babylon, this pagan religious celebration spread throughout much of the world.
The Druids of ancient Britain also borrowed this Babylonian festival and celebrated it to honor Samhain, Lord of the Dead, whose festival fell on November 1. - Halloween Through the Centuries, Linton, p. 4. They believed this pagan god called together "certain wicked souls on Halloween" - Encyclopedia Britannica, 14th ed., Vol. 11, p. 103.
Although Halloween poses as a Christian holiday, it is exposed as a pagan feast. One dictionary describes "pagan" as: "One of a people or community observing a polytheistic religion." "Polytheistic" means "the worship of or belief in more than one god." True Christians should consider these things as serious because God views these things very seriously. (Lev. 19:2) God Himself said: "You must not have any other gods against my face. Because I Jehovah your God am a God exacting exclusive devotion." (Ex. 20:1-5) NWT
Yet some may wonder what harm could possibly come from letting children attend a costume party or simply participate in a superficial way. Yes, it is not Scripturally wrong for children to have a costume party or play games such as bobbing for apples. However, doing so as a part of Halloween would be celebrating that pagan religious feast. This would be compromising Christian principles. The Bible condemns the whole idea of putting a Christian mask on a pagan practice.
If pagan ceremonies, customs, god names, etc. are really mixed in with ceremonies, customs, etc. that we use today, they are not merely unacceptable - - - they are detestable to God. We must completely get away from these unclean things and not even "touch" them. (2 Cor. 6:17) Notice how exclusive the worship of God must be: "Be careful to do everything I have said to you. Do not invoke the names of other gods; do not let them be heard on your lips." - Exodus 23:13, NIVSB. Also see: What Does the Bible Really Teach? - Take Your Stand for True Worship from the Watchtower Bible and Tract Society (WBTS).
Halloween and Witchcraft
The real religion celebrated by the "Holy Evening" of Halloween is still a living religion. What is sometimes called "witchcraft" has had its ups and downs but is still practiced as a religion in nearly every country of the world.
"It began in the shadowy darkness of man's early religion. It lived and flourished through the ages and it is by no means wiped out even yet. Witchcraft in the Middle Ages was the `art' of controlling natural forces by power obtained from the Devil. Witches were people who made agreements with the Evil One." - Britannica Jr., 1957 ed., Vol. 15, pp. 131-132.
Whether deluded or not, these "witches" were (and are) making a public declaration: a demonstration of their faith and a defiance of the God of the Bible. They continued to practice their religion (in many different, varying sects) in spite of great persecution. This religion of the Middle Ages actually grew out of the earlier pagan Druid religion.
The Truth About Halloween (AWAKE! SEPTEMBER 2013; JW.ORG)
The Origins of Halloween—What Does the Bible Say About Them? (JW.ORG)