Why did they go to see the happy medium in chapter five

The new planet they are on is gray and nondescript. Mrs. Whatsit tells Meg that they have come to see the Happy Medium and that she will show them their own planet. Deep within a cave, next to a fire, they meet the Happy Medium, a woman dressed in a long, purple satin gown holding a crystal ball. They all introduce themselves and Mrs. Whatsit tells the Medium to show the children their own planet. The Medium doesn’t want to because she’d rather look at things that are more “delightful,” but Mrs. Which tells her that soon there “will no longer be so many pleasing things to look at if responsible people do not do something about the unpleasant ones.”