Do you agree that Atticus' closing argument is the heart of Harper Lee's To Kill a Mockingbird? Explain with reference to: the deeply ingrained...

I firmly agree with the idea that Atticus' closing speech during the Tom Robinson trial is the heart of Harper Lee's To Kill a Mockingbird, as it touches on all of the central themes in the book: racism, prejudice, class, gender, and the legal system. Below, you'll find my opinions on how Atticus' speech relates to the three topics you've outlined in your question.

Southern Prejudice: Early on in his speech, Atticus asserts that the Tom Robinson case "should never have come to trial. This case is as simple as black and white" (205). Atticus says the case should never have come to trial because Robinson is obviously innocent. If he were a white man, he would have been set free without a trial (he may not have even been accused in the first place) since there was no evidence of rape occuring; however, as a black man, he is doomed to be treated unfairly and subjected to an unfair trial weighted against him. That's why Atticus says the "case is as simple as black and white." The very fact that the case has come to trial is proof that Southern prejudice against blacks has great influence, as the case only came to a trial to needlessly condemn a black man.

The Social Status of African Americans: Toward the middle of his speech, Atticus describes Robinson as "a quiet, respectable, humble Negro who had the unmitigated temerity to 'feel sorry' for a white woman" (207). In this statement, Atticus alludes to the fact that no one would expect a black man to feel sorry for a white woman, as black citizens were believed to be socially inferior to all white people. He uses this statement to then argue against the idea that all black people are of an inferior moral nature, asserting that all people are equal, regardless of race (207). In a nutshell, therefore, Atticus uses his speech not only to expose the racism directed against African Americans, but also to refute it. 

The Justice System: Finally, in the closing lines of his speech, Atticus claims that, in the United States, "courts are the great levelers, and in our courts all men are created equal" (208). In short, Atticus claims that the Justice System should be an institution that looks beyond prejudice and racism, and so he implores the jury to transcend the bigotry that brought the case to trial in the first place. This idea is a note of optimism, a tragic plea for help against the tyrannical forces at work in the world, and it concludes perhaps one of the greatest speeches in contemporary literature.