In A Wrinkle in Time, the earth is fighting a dark shadow, which is Evil, the Power of Darkness. This evil is manifested in hatred, war, and ignorance. How can one fight such a darkness? Mrs. Whatsit offers the children an example of someone who has, Jesus, who fought darkness and evil with love and faith. Charles and Calvin offer names of others who have fought the darkness: Da Vinci, Michelangelo, Shakespeare, Bach, Pasteur, Madame Curie, Einstein, Albert Schweitzer, Gandhi, Buddha, Beethoven, Rembrandt, and St. Francis. Then Meg offers Copernicus as an example. What do all of these people have in common? They all fought evil by creating beauty, advocating peace and love, or fighting ignorance by seeking knowledge. The idea is that they have lit the way for others who must also fight the darkness. Darkness is a metaphor for evil, and thus, light is a metaphor for its opposite, goodness. The only way one can conquer darkness is with light, and the only way one can conquer evil is by doing good.
they are lights for others to live by because they are fighting the black thing with their talents and since the black thing is an enemy people admire that these artists are trying to go against it