Pete Dray wrote this for a 2011 event at Durham University. One of the most helpful reflections on Halloween I've seen... Why God loves Halloween. Read the whole thing, or just taste this extract
"What has happened for centuries on All Saints’ Eve – or Halloween – is quite simple. God’s people act out a drama – a drama in which the demonic realm tries one last time to achieve victory, but is seen for what it really is. What is the means by which the demonic realm is seen for what it is? In a word: mockery.
According to the Bible, the devil’s great sin (and our great sin) is pride. And so, to remind themselves of Satan and the evil realm’s ultimate defeat because of Jesus’ death and resurrection, Christians ridicule them. In fact, this is why the Medieval custom arose of portraying Satan in a ridiculous red suit with horns and a tail. Nobody thought that the devil really looked like this; indeed, the Bible teaches that he is a fallen arch-angel. Rather, the idea of portraying the devil in this way is to ridicule him because he has lost the battle with Jesus and he no longer has power over us.
Similarly, on Halloween, the custom arose of mocking the demonic realm by dressing children in costumes. Because the power of Satan has been broken once and for all, children can mock him by dressing up like ghosts, goblins, and witches. The fact that Christians dressed up their children in this way shows our supreme confidence in the utter defeat of Satan by Jesus Christ – there is no fear!"