I find that one of the most compelling aspects of Achebe's novel is the way the reader is brought inside the culture of Umuofia in order to understand it from the inside out. In this sense, I find the use of the term "mythology" a bit misleading, since in Umuofia the stories and practices that we might identify as "myth" in fact play a vital role in the daily lives of the people and form a historical practice that we as readers of the novel grasp but which outsiders, like the missionaries, can't comprehend.
Take, for instance, the episode in which Enoch "unmasks" one of the egwugwu. The egwugwu are the living gods of the clan; even though to the Christians they are simply men wearing masks, to the people of the village, they represent the highest divine authority. When Enoch attacks one and reveals the man underneath the mask, this desecration does not show that the egwugwu are frauds but instead causes the other gods to rise up in anger. As a result, the gods of Umuofia gather in force and burn the Christian church to the ground. While the missionaries might see this as a form of mob violence, for Umuofia this act is a form of divine justice.