To reduce this story down to a one word theme, we might identity the theme as "change" or, in a phrase, "the morality of change". However, a more extensive reading of the theme allows us to identify a number of ideas related to change that are expressed in this story.
Resistance to change and insistence on change are attributes that help to polarize Julian and his mother. She holds a nostaligic and idealized view of the past, of childhood, and of the way things once were in general.
Julian’s mother relies on custom and tradition for her moral sensibility...
This resistance to change appears in her attitudes, her dialogue and in her behavior. It is exactly this desire to act as if race relations have not changed that leads to her being beaten with a hand bag.
Julian is the opposite of his mother in this regard.
He dismisses her notions of proper conduct as part of an old social order that is not only immoral, but also irrelevant.
He insists that things have changed and that they should change. Julian cannot tolerate his mother's nostalgia, though he admits to yearning to see the house that she often mentions. For Julian, change is a positive fact and a facet of reality.
These divergent attitudes concern many types of change. Financial change, aging, social change and geographical change are each dealt with in the story. The polarity of attitudes in regards to these changes constitutes both the central thematic idea of the story and provides the story's conflicts.