The night is far spent, the day is at hand: let us therefore cast off the works of darkness, and let us put on the armor of light (Romans 13:12).
It is well known that the name Halloween is simply a shortened form of Hallowed Evening, but there is nothing very hallowed, or holy, about this particular evening. Although it has been sort of Christianized by some as an All Hallows Eve preceding what is called All Saints Day, neither its origin nor its observance is Christian in any way.
Halloween has been observed as a pagan festival since long before the time of Christ, especially by the Druids in England and Ireland, but probably by the Celtic people in western Europe even before that. The craft of witches and sorcerers (including the modern Wicca cult) has always focussed on it as one of the key days of their nature religion. Among the Druids, it was observed with all-night bonfires and the supposed incarnate manifestation of the god of darkness, as he called his followers together for worship.
It does seem anomalous today that even many evangelical Christians have come to regard Halloween as sort of a harmless holiday on which to play games and dress up in masks and occult-theme costumes. These at least imitate and attempt to minimize those works of darkness which Paul exhorts us to cast off. Have no fellowship with the unfruitful works of darkness, he says in another place, but rather reprove them. For it is a shame even to speak of those things which are done of them in secret (Ephesians 5:11,12). Prove all things; hold fast that which is good, Paul says in yet another place. Abstain from all appearance of evil (I Thessalonians 5:21,22). Put on the whole armor of God, that ye may be able to stand against the wiles of the devil (Ephesians 6:11), for the devil walketh about, seeking whom he may devour (I Peter 5:8). HMM