What do Jesus, da Vinci, Michelangelo, Shakespeare, Beethoven, St. Francis, and Copernicus have in common in A Wrinkle in Time?

All these
historical figures are examples of Earthlings who, according to Mrs.  Whatsit, Mrs. Which, and
Mrs. Who, fight the Black Thing. Mrs. Whatsit, Mrs. Which, and Mrs. Who explain that the Black
Thing tries to take over planets, including Earth. Meg has...