Where in Harper Lee's To Kill a Mockingbird does Atticus act according to righteousness or justice?

Being righteous can be defined as behaving in a moral and upright way (Random House Dictionary, 2016). It can also be defined as deeply feeling anger towards something one thinks is immoral or unjust (Longman Dictionary of Contempory English, 2015). The word anger can be difficult to define; it's more than just the intense, often irrational, emotion we see every day. Being angry can be defined as feeling strongly displeased by something we know is "wrong," "unfair, or "painful" (Random House Dictionary, 2016; Cambridge Academic Content Dictionary, 2016). Anger is expressed in a combative way, but that act of combat can be expressed in a calm and rational way or in an aggressive and irrational way. While we never see Atticus express anger in an irate, irrational way, we do see him speak out for social injustices with the purpose of combating social injustices. It is in these moments that we see him behave righteously according to the above definitions. One example can be seen in his closing remarks to the jury in Chapter 20.

Towards the end of his closing remarks, Atticus points out that human beings are not truly equal in the ideal sense that Thomas Jefferson spoke of. In reality, we are created unequally due to differences in mentality, differences in education, differences in talents, differences in social class, and differences in race. He further points out that it is the court's job to create equality by treating all men as innocent until proven guilty. He further points out the weaknesses of the court system by asserting that the likelihood of upholding justice completely depends upon the characters of the men serving on the jury, as we see in Atticus's following remark:

Gentleman, a court is no better than each man of you sitting before me on this jury. A court is only as sound as its jury, and a jury is only as sound as the men who make it up. (Ch. 20)

In speaking of inequality, Atticus is protesting against inevitable social injustice, especially as a result of prejudices; he particularly speaks of social injustices when he speaks of inequality among races and social classes. In questioning the characters of the members of the jury, Atticus is protesting against the fact that jury members' decisions, especially in cases like Tom Robinson's, are usually clouded by racial prejudices. He is further trying to combat against the racist opinions of the jury members by reminding them, in his calm and rational way, to consider the facts of the case in an objective manner, not based on their subjective racist opinions. Hence, as we can see, Atticus uses his closing remarks to display a sense of righteousness by behaving in a moral way and by attempting to combat against immorality and injustice.