"And that ye may put difference between holy and unholy; and between unclean and clean." (Leviticus 10:10)
It is well known that the term "Halloween" associated with this date is a contraction of "Hallowed Evening," so-called because in the early medieval church, it was the evening for the vigil before "All Saints Day" on November 1, when all the designated "saints" of the church were especially to be remembered and honored.
Why this date was chosen is not clear, but it may be significant that many pagan religionists were also remembering their dead on that date, while also believing that their departed spirits returned at that time to interact in some way with the living. Especially prevalent among the Druids, this belief merged in many ways with the practices of ancient witchcraft, which also involved spirits, wide use of bonfires, and many questionable activities on that evening. In modern American popular usage, Halloween customs have evolved into "ghostly" parties, artificially "haunted" houses, and a childish protection racket ("trick or treat"). The "holy evening" is now at least "unholy" -- not necessarily wicked but certainly not God-honoring.
The warning of Moses and Aaron to the ancient religious leaders of Israel would perhaps be appropriate even today. There should be maintained a very clear and real "difference between holy and unholy."
"Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing" (II Corinthians 6:17). This is not a legalistic dictum for salvation, but should at least be carefully considered in terms of one's Christian witness. "Let every man be fully persuaded in his own mind" (Romans 14:5). "For the kingdom of God is not meat and drink; but righteousness, and peace, and joy in the Holy Ghost" (Romans 14:17). HMM