Justice...that's huge. If this is an essay, you're going to have to narrow your thesis.
The novel deals with justice and prejudice throughout. The title basically captures the whole theme of the book: it is a sin to kill a Mockingbird. Atticus tells his children this. The reason--mockingbirds do nothing bad--they just sing. There are a couple of "mockingbirds" in the story--Boo, Tom Robinson. Both these men are innocent victims of the town.
A few brave people try to do the right thing. Atticus seeks justice for Tom by opting to defend him in court (Tom is being tried for a rape he did not commit). The jury convicts Tom because they essentially believe the white woman who accused him.
Boo is in part a victim of his father's idea of what is just. Instead of being sent to a state school, his father keeps him under house arrest--a punishment that last Boo's entire life.
Boo risks everything when he saves Jem and Scout. When he stabs bob Ewell (Mayella's abusive father), it is the right thing to do--he saves Jem's life. However, if justice were served according to the letter of the law, Boo would have gone to jail for what he did.
Both Heck Tate (the sheriff) and Atticus decide to lie to save Boo from the consequences of his action. Atticus lies and says that Jem did it (knowing Jem is still too young to stand trial) and Heck Tate lies and says that Bob Ewell "fell on his knife". This means that both of the men who are sworn in one capacity or another to uphold the law are willing to bend it to protect a vulnerable person. So there is humanity in the justice in the book. It shows that there is a type of justice that goes beyond the courts, and that sometimes the "right" thing is not upheld by the law.
An underlying theme in this book is that we as humans are responsible for acting according to our conscience. We should try to use the law when we can, but we also have a higher imperative--we have to follow our conscience.
It is important to note that in To Kill A Mockingbird, the presence of injustice is used to demonstrate the need to pursue justice. This is evident on all levels- from the most serious levels involving Tom Robinson's clearly unjustice trial down to things that seem trivial such as the injustices Scout sees in her first grade classroom.
This story has endured largely because of the realistic circumstances of the injustices. Note that while Atticus strives for justice and is certainly a noble man, he is not able to right all the wrongs of the world; in fact, he is not even able to keep injustice from his town where he is a man of notable stature. The ending might lead a legal purist to say that justice was not truly served, but the decision to protect Boo Radley seems to the reader to be justice in a higher sense.
someone help me please??