The brownstone houses are significant as repositories of human history. Prior to the West Indian migration en masse to Brooklyn in the 20th century, the brownstones had been largely inhabited by white families. As the story begins, the houses still stand proudly in their unique fashion. They resemble an "army massed at attention" and are formidable in their red-brown stone uniformity.
Despite this superficial homogeneity in design, the narrator notes that each house is unique in its own way. Many houses boast Gothic, Romanesque, Baroque, Greek, and Victorian elements in their designs. By 1939, the white inhabitants of the brownstones were replaced by enthusiastic West Indian families, eager to assimilate into American society and equally eager to reap the material rewards of being contributing members of that society.
While Selina revels in the ghosts of the past, she also knows what the brownstone house represents to her mother, the irrepressible Silla Boyce. Like so many of her ambitious West Indian neighbors, Silla intends to embrace the American Dream as her own. She intends to work relentlessly, scrimp mercilessly, and save abundantly in order to achieve her dream of "buying house." To Silla, ownership of the brown house is definitely a means to an end.
Silla and her West Indian community see the brown houses as representations of their ambition to be unique members of American society. They want to be differentiated from the black community in Brooklyn, who they regard as "keepbacks," and they mean to achieve upward mobility through sheer hard work. Like the houses they inhabit, these West Indian immigrants resemble an "army massed at attention." They intend to succeed, and they mean to duplicate the success the previous white inhabitants enjoyed.
So, the brownstone houses are significant not just as repositories of human history, they are also indirect representations of West Indian ambition.