In both The Wizard of Oz book and film, there are two wicked witches – one from the East and one from the West. And in both versions, when Dorothy lands in Oz, she is greeted by a good witch, but the two stories disagree on who she is. According to the book, it’s the nameless Good Witch of the North, but in the film, it’s Glinda (Billie Burke), also referred to as the Good Witch of the North. However, in the book, Glinda is actually the Good Witch of the South, and Dorothy doesn’t meet her until she goes looking for her in the final chapters.
By combining the two characters, the film eliminates the need to introduce another character late in the story and ensures that Glinda is a reliable force for good throughout. However, this also creates a small plot hole: Glinda gives Dorothy the magic Ruby Slippers early in her time in Oz, but doesn’t reveal that they have the power to bring the girl home until after she’s gone through many trials and tribulations, and left the Openly question why Glinda Dorothy endured so long. It’s like Obi-Wan gave Luke the lightsaber on Tatooine but never showed him how to turn it on.
In the book, the Good Witch of the North has no idea what the shoes are capable of, so it’s more understandable that Dorothy doesn’t end her long quest in Oz until she meets Glinda at the end of the book.