A number of themes are explored throughout Lee's To Kill a Mockingbird Such themes include good & evil, respect and human dignity along with a number more as you can find below.

Good & Evil

Throughout To Kill a Mockingbird only two characters are seen as being completely good as juxtaposed to the amount of evil in Maycomb. Atticus and Boo Radley are these characters and throughout the book these people are used as a platform to attempt to better the other characters. Atticus is seen as a father figure, enforcing his views on his children and this teaches them from a young age the distinction between good & evil and right & wrong.

Childhood & Growing Up

The fact that it's a sin to kill a mockingbird is used throughout the novel, especially throughout this theme. Mrs Dubose suffers from an addiction around chapter 11. This character allows Atticus to explain to his children what real courage is, not a man with a gun but someone on the door-step of death.
This addiction allows the book to compare how Jem has grown up, in a sense as compared to how he was previously.
Jem leads the phase of transition towards maturity in the novel. Towards the begining Jem and the majority of underage characters seemed imature. Such examples of this imaturity include the game they played, mocking the Radleys. However as the novel continues Jem becomes quite more mature, to a point where he asserts dominance over the other children.

The Existence of Social Inequality

Throughout the novel, the reader is made aware of the social status that is determining where society places different individuals. There is an overcomplicated social hierachy in Maycomb, and this determines how the case, in particular is conducted and the decision that is made about the accused. We are brought two main examples of two very different families in different statuses.
We become aware that the Finches are a well-off family who are respected and known by the people of Maycomb. However Tom Robinson's family, being "black" is considered to be at the bottom of the social hierachy. They are not respected and trusted by many people in Maycomb.

Small-town Life

In the novel, small town life is a very dominant theme as the setting takes place in a small country town of Maycomb. An important part of the novel is when Miss Maudie's house sets on fire. All the people of Maycomb rush to help, and try to get Miss Maudie's possessions out before they were ruined. This automatically portrays to the reader that the town consists of one big family where people are willing to help each other in times of need and desperation.
Small town life is also portrayed through the novel through the quote that states; "There was no hurry, for there was nowhere to go, nothing to buy and no money to buy it with, nothing to see outside the boundaries of Maycomb County."PG 6. This quote states that the people had always lived in Maycomb and that they were content to continue living a small-town life.

The Importance of Moral Education

In the beginning of the book, until the ending, we learn about the importance of moral education to the Finches family. The major example of this is Scout's detemination to keep reading with Atticus. This is expressed when Miss Caroline rigidly comments on the educational techniques that Atticus was using to teach Scout how to read. Scout returns home, with low spirits and after recounting the day's events to Atticus, to her delight Atticus had proposed that they make a compromise. This was extremely important to Scout as she enjoyed reading with her father and wanted him to continue teaching her his ways.
Atticus and Scout Finch