What is is the main theme in chapter 4 (The Black Thing) in "A Wrinkle in Time"?
In chapter four we see a very stark contrast in the idea of good versus evil. The children are presented with some beautiful examples of "good", the visual beauty of the the planet, Mrs. Whatsit's true form, and the singing of the other creatures. As Mrs. Whatsit carries the kids higher into the atmosphere, they are presented the other side of Uriel. From here, the children have a good view of the dark thing that threatens to encompass everything around it. Although they do not know for sure what it is, Meg certainly recognizes it as evil personified, something that gives her a very bad feeling.
This chapter presents us with the opposing forces inherent in the rest of the novel. Meg sees some of the beauty of the world and is able to transfere that into feelings of love, which will be her ultimate weapon in victory at the end. In comparison, she is able to see how great and large evil is and can be, how tough it can be to defeat.