What does the reader learn about Atticus's character during his summation to the jury in Lee's To Kill a Mockingbird?

In Chapter 20, the reader learns that Atticus Finch is the moral compass for Maycomb County.

Throughout the narrative of To Kill a Mockingbird, Atticus Finch is consistent in his adherence to moral principles, practicing the precept of "climbing into the skin [of a person] and walk[ing] around in it," as he is polite to Mrs. Dubose despite her insults, he addresses the Ewells professionally and politely despite their false testimonies, and he always treats everyone fairly regardless of a person's race or social status. Moreover, Atticus remains stalwart in the practice of these personal convictions regardless of the situation, even when he is maligned and ostracized by the community for having taken the assignment of defending Tom Robinson.

In his closing argument at Robinson's trial, Atticus reminds the jury of every citizen's Constitutional rights, regardless of his color or creed or social position. He appeals also to their moral consciences, subtly suggesting that they follow his example: "In the name of God, do your duty."