It all comes down to understanding yourself, and others.
Atticus has a young daughter, Scout. Like most dads he wants give his daughter a real life education not just an academic one. One line from the movie is most riveting:
If you can learn a simple trick, Scout, you'll get along a lot better with all kinds of folks. You never really understand a person until you consider things from his point of view, until you climb inside of his skin and walk around in it