Cultural heritage
Black Elk does not believe he is simply preserving a costume. For him, culture goes way below the skin, into the inward parts of the human soul. His journey is a martyrdom at the hands of the US government through which Black Elk is made to suffer and witness the horrible truth that he gradually begins to admit—that Native culture is being systematically eliminated by the government through harassment and relocation. The white soldiers have no idea that these people's culture ties them to their land in a deeply spiritual way that cannot be easily removed.
Idealism and tragedy
If this tragedy involves any kind of hubris, it is probably the hubris of idealism. Black Elk has powerful religious experiences which open his mind to an ideal way of life, an ideal outcome, and although he has his hesitations, he comes to believe because of ecstatic religious experience that the purpose for his ideal visions is to manifest them in real life through his own work. This leads to a terrible tragedy where he is martyred by fate (and the US government), but he still blames himself, wrongly believing that it was his fault that the Native American culture does not survive. More technically, it's actually more of a United States government issue, not a personal reflection of his merit.
Personal calling and revelation
Without a doubt this book focuses on Black Elk's prophetic shamanism, featuring his tales of dramatic and full-blown religious experiences and their descriptions. He even attains spiritual abilities for healing and navigating spiritually complicated situations—to the point of fame. His life is a portrait of the power of powerful religious awakening in a person's life. By the time he states that he firmly believes the gods and his ancestors intentionally revealed his calling to him, the motif is accomplished: he is a shamanic prophet with a leadership role in his community, a leadership role that seemingly stems from his authoritative spiritualism.
