The theme of 'Good vs Evil' is shown throughout the film 'The Wizard of Oz' in different ways.
The evil is first shown at the start of the film when the neighbour tries to steal Toto from Dorothy. This theme of 'evil' features through the rest of the movie by having the two wicked witches, of the East and West. The way the Wicket Witch of the West tries to get the ruby slippers off Dorothy several times and kill her.
The times good was displayed in the movie included when the Witch of the East is killed, the Witch of the West is killed and when Dorothy helps other people e.g. when she helped the scarecrow down from the pole and when she and the Scarecrow poured oil on the Tin Man to get him moving. There are also times when other people help Dorothy. Glinda the Good Witch and the Munchkins who tell Dorothy what to do.
In this scene you can see the 'Good' winning over the 'Evil'.
In the above scene The Wicked Witch of the West has cornered the group and is now trying to kill them but as usual good overcomes evil and Dorothy kills the witch.
This is an important theme because it shows that good generally overcomes evil and even little gestures of good have an impact on peoples lives.