good vs evil the classic theme in a lot of fairy tale story's, the good vs evil in oz shows a battle between the wicked witch of the west and the good witch of the north and also the wizard of oz although he not really a good character. near the start of the story line Dorothy's house was swept up in a hurricane with her and Toto her Cairn Terrier canine, the theme of good vs evil really sets up the book and how Dorothy comes upon here quest and all the road blocks she faces on her journey.
good vs evil is one of the more important themes in the big as it brings out some real plot twists that if they weren't resolved could've ended badly, for example when the wicked with west captured Dorothy and the lion which nearly got the lion killed as she was putting the lion through some pretty evil stuff really showed the battle the the crew faced and also how the overcome the bad and keep the positive things alive.