Calpurnia means just because Scout's family might be better off, wealth and class wise, than the Cunninghams Scout cannot go around treating them as if she is above them or has a higher rank. Calpurnia is correct and is trying the kids perspective of the Cunningham's point of view and adding her experience to back up her lesson, with emotion, since the kids visit a colored Church ever so often.
The best part of the novel is the one that says- Night found him leg weary with hands and face lashed by the branches. that explains and supports the idea
