Quote 1
"The only remedy for this is not to let it beat you." (1.33)
Atticus is talking about arthritis here, but this philosophy could be applied to any fight he gets into. He won't let anyone beat him, at all, ever. He is completely rigid, even in old age.
Quote 2
"Jefferson believed full citizenship was a privilege to be earned by each man." (17.89)
Here we start to learn that Atticus is a man who puts political principles ahead of human ones. Considering how coldly he comments on a family member's death early in the book, that shouldn't come as a surprise.
Quote 3
"As you say, Jean Louise, there's only one thing higher than the Court in this country, and that's the Constitution." (17.52)
The 10th amendment changed the Constitution. Rules change, but men like Atticus never do.