It's Wrong for Christians to NOT Participate in Halloween!
In all honesty that title may have been a bit of a click-bait ploy...
That being said I have every intention of making a point along the lines laid forth in the title.
Throughout the Bible the people of God are described in many ways. One of the more common ways the people of God are described is as a "light to the world" (Matthew 5:14, Isaiah 49:6, Genesis 26:4). From the beginning, God's interactions with his chosen people has been one where they are to shine forth the glory of God to the world. When God brought Israel out of Egypt he did so in order that the nations might see his righteousness lived out in their community.
The law that was given to Moses on Mt. Sinai was not a law that was meant to build a preventative barrier between the "clean" Israelites and "unclean" gentiles. In fact, this is one of the main sins that Jesus confronted in his earthly ministry. The Jewish "nation" that Jesus confronted in the first century was one that was under Roman authority. When Jesus confronted this world he told them that he would show them the "sign of Jonah" (Matthew 12:38-45). When Jesus said this he was making a very pointed critique of the Jewish leaders and the Jewish society he was confronting.
The story of Jonah is a very important one to understanding the life and ministry of Jesus. Jonah was a very unwilling prophet. The reason Jonah was so unwilling was because God had called him to go and prophecy to Ninevah, the pagan, ungodly capital of Assyria. Jonah knew that God's prophets were His word to His people. If God was going to send him (Jonah) to prophesy to another people then Jonah knew that God was bringing judgement on his people by no longer speaking to them through His prophets.
When Jesus tells the Jewish leaders that they will receive the sign of Jonah, one of the things he is communicating to them is that God is leaving them. In the same way that Ezekiel saw God leave the temple in Ezekiel 10 God was again going to leave the temple and go to the gentiles. We see this more clearly in Jesus' great commission (Matthew 28) and in the story of the book of Acts.
The reason God determined to leave this people (the sign of Jonah) was because they refused to leave themselves and be the evangelical community he had called them to be. They were not being a light to the gentiles (the Romans) like they should have been.
This may seem like a severe judgement to our overly-sentimental modern and western eyes but if we take a second to step out of our current presuppositions and into the story of scripture we will understand it a little better.
The Jewish nation was called to be a priestly nation to the world; teaching the world and mediating God's goodness and mercy to the world. The world (outside of God's covenant) does not know how to live. God has revealed fullness of life to his people (in the Law and the prophets in the Old Covenant, and infinitely more in the person of Jesus in the New Covenant). The covenant people of God are therefore to take this knowledge and display it to the world that so often gets it wrong
The world has not been given God's definitive word on how to act in so many different arenas. They do not know how to act when it comes to relationships, sex, consumption, clothing, gender, society, celebrations, worship, etc. The covenant people of God have been taught how to act in these areas. One of the principle ways in which the covenant people of God were called to be light to the world is through proper conduct in every area of life as a display to the world. They were to teach the world how we are to live in the world that God had made. This displaying serves in a priestly manner to transform the world.
When the covenant people of God refuse to act in accordance with God's word in all these ways they not only damage themselves, they also abandon the world to the powers of their own sin and Satan. God loves the world too much to allow the disobedience of his covenant people to doom the world. Therefore, throughout history, God has shown his people the sign of Jonah. This sign serves as a judgement to the people of God but as salvation to the world; after all, Nineveh saw great revival under the reluctant prophecies of Jonah. Moreover, the world has seen and will continue to see great revival under the relentless greater prophet/Jonah, King Jesus.
We must learn from all this when it comes to Halloween and other such things. Of course the world gets into all sorts of trouble with Halloween, Christmas, alcohol, sex, etc.. That's because the world doesn't know how to celebrate and use the good gifts that God has given us. The world's celebrations are filled with drunkenness and debauchery. In contrast, the covenant people of God have been taught how to celebrate for thousands of years (we are actually suppose to learn how to celebrate each week in the Lord's Supper).
Too often Christians take a dualistic approach to these matters. Either we shun the evil commercialization of Halloween, Christmas, Easter, etc. and retreat to our churches for "Trunk or Treat" or we embrace the worldliness of it all because we are "free in Christ" and get hammered on pumpkin flavored cocktails. Christians need to display true celebration and festivity to the world during Halloween, Christmas and Easter by showing the world how God has taught us to celebrate: eating, drinking, dancing, and singing all with thankfulness in our hearts to God.
When the people of God act faithfully in this, God gives richly to us in our festivals. When we act unfaithfully in this, God either takes away our festivals (often through our own self-imposed shunning of them) or gives us over to the enslaving nature of the world's festivals.
So in conclusion, Christians should participate in Halloween. But not only Halloween. Christians should be teaching the world in everything. Christians should drink because the world doesn't know how. Christians should celebrate Christmas with trees and lights and gifts because the world doesn't know how. Christians should celebrate sex within marriage because the world doesn't know how. It is part of our priestly duty (as a kingdom of priests) to show the world how to live and so win them over to Christ.
Food for thought.
Postscript – Obviously, none of what I am saying is condoning foolish participation in the worldly ways of Halloween. Further, because man is sinful, Christian festivals like "All Hallows Eve" (Translation "All Saints Eve" [the eve of All Saints Day, like the eve of Christmas]) have been transformed in many places (San Francisco, etc.) into a community-wide display of human depravity. This post looks to serve in a way that would call Christians to return to their roles as mediatory priests for the world rather than a people that either embraces or retreats from the world.