This conversation happens in Chapter 9, as the Robinson trial is gaining attention. Scout has been fighting at school because of the names other children are calling her father. Even though she doesn't fully understand the implications of these names, she knows that they are an attack on her father. Atticus knows that this trial will continue to cause tensions in the children's lives. Maycomb's disease is racism, rooted in hatred and ignorance. Atticus has been trying to teach his children equality, tolerance, and understanding. These lessons extend beyond race and deal with respecting individuals for who they are regardless of race, gender, background, etc. This trial is going to be the biggest test of those lessons for the Finch children.