Atticus Finch is dedicated to a set of ideals, including a strong sense that justice should be defined that same way for people of all background and races. More generally, Atticus believes in fairness as the backbone of justice. We can see this attitude in a number of places in the novel.
Atticus gives up shooting despite his prowess with a gun. This is due to his belief in fairness, according to Miss Maudie. This egalitarianism is generalized in his character and in his social attitudes.
[Atticus Finch] refuses to use his background as an excuse to hold himself above others and instead is a model of tolerance and understanding.
In dealing with Jem and Scout, Atticus is also fair. He listens to both sides of a conflict before making up his mind on who is to blame. He often seeks to make compromises with and between them.
Atticus' sense of the necessity of fairness in legal justice is clearly demonstrated in his vigorous defense of Tom Robinson in court.
Atticus's own actions in arguing the Robinson case demonstrate this kind of courage, and his behavior throughout embodies values of dignity, integrity, determination, and tolerance.
Despite the difficulty and danger of defending Tom Robinson, Atticus feels that he must do his utmost in order to maintain the respect of his children. He explains himself repeatedly and says that he must be an example to his children in his actions and this animates his passion for justice as much as his ideals do.
Atticus was a fair man, and he knew what God wanted him to do.