What is the purpose of the character Boo Radley in the book?please include a couple quotes

As one of the symbolic mockingbirds of Harper Lee's novel
and as the impetus to the maturation of Jem and Scout, Boo Radley plays an integral and
unifying role in To Kill a Mockingbird. For, he advances the
development of an adult perspective for Scout and Jem, as well as contributing to the
development of the themes of Tolerance/Prejudice and of
Knowledge/Ignorance.

Threading throughout the narrative are
episodes about Boo Radley, who is first perceived as one of the "haints" that the
children superstitiously fear.  From the scoldings and explanations of Attucus,
they come to understand that Boo is really a man, albeit a strange and reclusive one. 
Later in the narrative, Scout and Jem perceive the kindness and wish for friendship that
Boo extends to them by rescuing Jem's pants from the wire fence, covering Scout with a
blanket against the cold, and by placing little gifts into the knothole of the tree that
the children pass on their way home. Finally, the heroic act that Boo commits in defense
of his friends teaches Scout the meaning of Miss Maudie's comment that Boo may just wish
to remain inside because as Dill says, "Maybe he doesn't have anywhere to run off
to....," since he understands "the evil that men do" [Julius
Caesar]. In the final chapter, Scout feels some guilt about the way that she
and Jem have first treated Boo, and she sheds all her prejudices about
Boo,

Atticus was right.  One time he said you
never really know a man until you stand in his shoes and walk around in them.  Just
standing on the Radley porch was enough.