This quote represents a conflict between tradition and progress.
Obi arrives at the school with hopes of modernizing the school where he has been appointed headmaster. He reflects that it is "backward in every sense of the word" and believes that he has a "grand opportunity ... to show these people how a school should be run." Obi's wife shares his vision for progress and modernization and begins planting beautiful bushes that make the natural shrubbery in the neighborhood look "rank" by comparison. In her efforts to improve the natural aesthetic of the grounds, she plants flowers and shrubs across a path used by the villagers.
In the above quote, a lone woman is spotted crossing the schoolyard in her journey between the village shrine and their sacred burial grounds. Obi feels that this is scandalous behavior and that she shouldn't be "allowed" on the school grounds to make this journey. The woman represents a world of tradition; the villagers have used this same path for so long that their journeys have carved out a visible history of their route in the earth.
Obi and his wife's efforts to improve this community block the traditional path the villagers deem vital to their way of life. This generates conflict between the villagers, who find great significance in traditions, and Obi, who believes that progress and modernization are much more crucial to the future of the community.