Picking up the story after a major event in it, like the expulsion of Satan and the fallen angels from heaven, follows the tradition of an epic beginning <em>media res</em>, in the middle of things. Homer did this first in the Iliad and the Odyssey.
The prefix "im-" usually means "not." Take for example the word imperfect. The prefix then causes the word to refer to something that is not perfect. Therefore, the word impersonal would mean that something is not personal. Meaning that personal thoughts and opinions/feelings are not involved.
Scout unknowingly diffuses the tense situation simply by being present and attempting to politely have a conversation with Mr. Cunningham. Walter empathizes with Atticus as a father, which is why he instructs the mob to disperse without harming anyone.
