This question is supposed to be answered in Chapters 4 and 5 of the book
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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.”
In the crystal ball, the children can see their own planet, but it is clouded by the Darkness they had seen earlier. Meg asks if it had just shown up, and Mrs. Whatsit tells her that it has actually been there for a long time. This explains why Planet Earth is so deeply troubled. They tell her that this Dark Thing is Evil, the “Power of Darkness,” but that their planet had been instrumental in fighting the Darkness through time. When Calvin asks who the fighters had been, Mrs. Who relates a quote: “And the light shineth in darkness; and the darkness comprehended it not.” Charles Wallace recognizes this as Jesus, and Mrs. Whatsit tells him yes, along with other great artists and scientists and thinkers such as da Vinci and Shakespeare and Einstein, as well as Buddha, Beethoven, Rembrandt, and St. Francis.
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