…some claim that marking All Hallows’ Eve may have originated as just such an occasion to “trick” Satan, the most prideful of all creatures, by giving him what is most offensive to his arrogance: mockery. As Luther would say, “The best way to drive out the devil, if he will not yield to texts of Scripture, is to jeer and flout him for he cannot bear scorn.”

David Mathis, from the article Trick or Treat? It’s Martin Luther

I’ve read this before. That dressing up scary-like was an attempt to make fun of the devil and his demons. I’m guessing American capitalist added the candy bit. See below: