In his closing speech, Atticus's diction—or choice of words—is measured and calculated. He begins by declaring to the jury that "This case is as simple as black and white." This is a common expression, meaning that something is clear-cut, but Atticus is aware of the subtext of this statement: this case is really about the color of the defendant's skin, pitting the word of a white woman against the word of a black man.
In the next part of his speech, Atticus uses emotive language to evoke pity for Mayella Ewell, the chief witness against Tom. This is an unusual strategy for a defense attorney to employ. Nevertheless, he reminds the jury that Mayella is "the victim of cruel poverty and ignorance." Here, Atticus is trying to make the jury understand the social circumstances of the case.
He subsequently uses a vivid metaphor to drive home this point when he talks about how Mayella broke the social code that said a white woman should not have sexual relations with a black man. He says that "No code mattered to her before she broke it, but it came crashing down on her afterwards." Atticus wants the jury to understand Mayella's reasons for accusing Tom, because if they can understand those reasons, they will see Tom for what he is: a victim and a scapegoat.
Later in his speech, Atticus uses irony when he states that Tom Robinson is guilty only of having "the unmitigated temerity to 'feel sorry' for a white woman." He wants the jury to understand that Tom Robinson is on trial for feeling sorry for a white woman, and he wants them to think about (or at least feel) how ridiculous that situation is. The word "temerity," meaning extreme audacity, is heavily loaded with sarcasm.
A little further on, Atticus draws upon the work of Thomas Jefferson and his declaration that "all men are created equal." Here, Atticus is appealing to the jury as patriotic Americans. He wants to remind them of the founding principles laid out in the Declaration of Independence: namely, the idea that all men—black and white—are equal in the eyes of the law.
He says to the jury that "in this country our courts are the great levellers, and in our courts all men are created equal." The deliberate repetition here of "our courts" is again to appeal to the patriotism of the jurors. He wants them to uphold one of the fundamental principles of the Declaration of Independence and reach a verdict based on the facts of the case rather than the color of the defendant's skin.