I think one of the most profound things about this speech is that Atticus does not necessarily do nor present anything in a way that is particularly "showy" or outstanding. His tone is firm and straightforward. Sadly, the case is cut and dry, yet he knows the jury will not be unbiased in their decision. He outlines exactly what must have really happened to Mayella, and essentially, why Tom has been incriminated but could not possibly be guilty. He restates the evidence in a very list-like and simplistic way.
At the very end however, Atticus dares address the so-called "elephant in the room" when he addresses the common white assumptions about "all negroes." He basically defines the blatant prejudice that clearly exists in this town and this case. He then sums everything up with a reminder that "all men are created equal" and that a United States courtroom should be the one place that this is true.
The entire speech is just perfectly delivered by the one man in town who has practiced as much integrity as he's asking for.