She gives Scout discipline: and it's more direct and to the point so it supplements Atticus' often philosophical, yet coherent lessons. One of the most significant things Cal does for Scout is to show her how to see things from other people's perspectives. She does this by scolding Scout when she makes fun of Walter for pouring syrup all over his food. Scout understands who's poor and who's not, but still needed to learn how to step into others' shoes. At the end of the novel, Scout stands on the Radley's porch, and for the first time, literally sees her street from the perspective of that porch: this is a literal change in perspective, but it is a metaphor that runs throughout the novel.
Most importantly, Cal is a mother figure and a link between the black world and the white world: and the different perspectives therein. Taking the children to church is one example where the children learn about this division/potential link. (They get a larger sense of the division at the courthouse). Cal certainly does signify, through her actions and who she is, the potential of a bridge between different worlds in the town: mostly between black and white, but the lesson also applies to class (income) divisions. Cal is THE mother figure in this book: more so than Miss Maudie or Aunt Alexandra.
Cal proves to be a bridge between white and black and she teaches Scout many things as well as manners. When Walter Cunningham comes over to their house, Cal teaches Scout that no matter what you shouldn't put someone down because you never know what their life is like and you need to show respect. She is a mother figure as well and she tries to make sure the kids have proper morals and no one person is better than another.