how does the man's appearance contrast with the sound of his voice

The man begins to talk to them in a kind and gentle voice, and Meg realizes that he is not talking to them with words but rather through their minds. The man’s eyes are bright with a reddish glow and Charles Wallace tells them not to look into those eyes or else they will “hypnotize you.” The man tells Charles Wallace that there are other ways to get into his head, and Charles Wallace threatens to kick him - clearly the first time Meg has ever heard Charles Wallace threaten anyone with violence.