Answer:
The man with the red eyes in the novel "A Wrinkle in Time" is frightening because he represents the ultimate evil and embodies all the negative qualities of the universe. He is the representative of the Black Thing, the embodiment of darkness, and chaos, and has the ability to control the minds of others. Moreover, he is described as having no discernible features other than his glowing red eyes, which gives him an otherworldly and demonic appearance.
Meg's experience trying to explain seeing to Aunt Beast highlights the limitations of language in conveying certain experiences. She realizes that some things can only be understood through direct experience and that words cannot always fully capture the essence of an experience. This realization challenges her assumption that knowledge can only be acquired through language and expands her understanding of the complexity of communication.
In the novel, appearances can often be deceiving, and it is not always clear when to trust what you see. For example, Camazotz appears to be a perfect, orderly planet, but in reality, it is a totalitarian dystopia controlled by the man with the red eyes. Similarly, Charles Wallace appears to be under the control of the man with the red eyes, but his true nature as a powerful individual with a unique mind becomes clear later in the story. The novel suggests that it is essential to look beyond appearances to understand the true nature of things.