Why does Harper Lee uses the character of Atticus Finch in To Kill a Mockingbird to show one the need for human compassion?
Without human compassion, what would become of our society? This theme is one of the most universally important themes, and our chance to read about and learn about this theme from such an admirable man as Atticus Finch provides us much pleasure in the reading of To Kill a Mockingbird.
Atticus Finch is an amazingly admirable and consistent character. He never fails to teach his children that no matter what a person looks like, or how a person acts (or seems to act) that person deserves to be treated with an appropriate amount of dignity and respect. Scout and Jem can certainly learn from Atticus's unfailing compassion for many of the other characters in the novel, and he uses various interactions as learning examples for his children.
When Scout treats Walter Cunningham rudely, Atticus makes sure that she understands that even though the Cunninghams are poor, doesn't mean they lack dignity and explains how to treat everyone at their dinner table in an appropriate way.
When Jem gets angry over Mrs. Dubose's hurtful comments, Atticus makes Jem read to her each afternoon. It is only after she dies that he reveals the Mrs. Dubose morphine addiction is what caused her temper and that Jem should admire the courage it took for her try to die free of the drugs.
It wouldn't occur to Atticus to NOT take Tom's case even though the outcome would be considered almost inevitable in the deep South of the 1930's. Atticus shows his children that every man deserves the best defense possible.
Atticus stops his children from playing the "Boo Radley" game because it is rude and shows a lack of truthful understanding of the circumstances of Boo's life.
There are numerous other examples of Atticus's behavior towards others and it is certain that Jem, Scout and all of us who read the novel can learn from the positive example he sets.