In Chapter 28, positive and negative themes are dramatized. The positive is where we like to focus: Scout and Jem were very brave as they walked home along, and their choice to proceed despite their fears shows us what bravery can be like—and that it is available to everyone, even children.
The negative themes are deceit and cowardice. Bob Ewell acts on these themes, seeking to kill Scout in the night—an adult attacking a child, a man attacking not the man he's angry at, but that man's child, etc. His actions show the depths that humanity can sink to.