The tragic demise of Native cultures in America
The white frontier armies who conquered the plains were despotic, and they treated the Kiowas with even more vilely perhaps because their language was so unapproachable to the white men. Therefore the religious rites of the tribe were subdued and the culture was placed under siege.
The finality of death
There is no getting around how sad the end of this book is. When he remembers how lively his grandmother was, Momaday brings attention to the absolute silence of her absence. Once a house filled with mirth and business, now the home sits as a vestige of days gone by. His grandmother's death indicates the final death of the Kiowa way of life.
Journey and self
Many, if not most, world religions contain a pilgrimage, either a pilgrimage that a person must make, or the people group's relocation in the distant path, like the Exodus story perhaps. For the Kiowas, this was their emigration from Yellowstone to Rainy Mountain in Oklahoma. This corresponds to Momaday's own journey of self discovery and rediscovery of his cultural background. He is willingly participating with the spirit of his ancestors on their sacred journey to Rainy Mountain.