Who said I wanted you to see what real courage is, instead of getting the idea that courage is a man with a gun in his hand. It's when you know...

said this about Mrs. Dubose,
who fought her addiction and won.

Atticus knows that his
children are struggling with the towns reaction to his defending Tom Robinson.  This is why he
sendsto read to Mrs. Dubose after he destroys her flowers.  He tells Jem he would have done it
anyway, because he wanted them to see Mrs. Dubose beat her addiction.

Mrs.
Dubose is a horrible mean old lady who lives on the Finches street.  She often insults them, but
when Atticus is defending Tom Robinson her insults get worse.

Yes indeed, what has this world come to when a Finch goes against his raising? Ill
tell you! She put her hand to her mouth. When she drew it away, it trailed a long silver thread
of saliva. Your fathers no better than the niggers and trash he works for! (Ch. 11)

Jems punishment for destroying the flowers is for Jem to go read to
Mrs. Dubose each night.  She sets a timer.  The amount that he reads gets longer and longer.  He
also notices that she is sharp at first, always correcting him, but the longer he reads the
quieter and sicker she gets.  Atticus tells him she was addicted to the pain killer morphine. 
She wanted to die having weaned herself off of it.

Atticus wanted to use this
a lesson about moral courage.  Courage is more than facing someone down with a gun.  It is
sticking to something difficult.

€¦ You rarely win, but
sometimes you do.  Mrs. Dubose won, all ninety-eight pounds of her. According to her views, she
died beholden to nothing and nobody. She was the bravest person I ever knew. (Ch. 11) 

This lesson is important becauseand Jem will have to face people
during the trial.  They have to understand why Atticus is doing it.  He is defending Tom
Robinson because it is something he believes is right.  It is worth doing, even if it is hard,
and even though it is going to be almost impossible to win.