The changing culture
Black Elk seems sometimes willfully ignorant of the changing political landscape around him. That doesn't apply to technical matters: he is obviously well-informed about the activity of nearby militaries, but in general, he seems to believe genuinely that there is a hope for Native American culture in the New America he watches unfold. The name for this dramatic irony is "hope." He does not know what will happen, but he chooses to believe that with correct action and religious sincerity, the gods might let their way of life survive. The reader already knows from history that he is largely incorrect.
The vision
It seems drastically ironic to a modern reader to encounter Black Elk's stories of religious ecstasy. The truth of the matter is that Black Elk's tribal and pantheistic opinion of spirituality is historically standard, but because of the modernization of the West, it feels very jarring to read about out-of-body astral projections into heavenly realms of one's own ancestors. The vision reported is catastrophic to the point of permanent identity change. Black Elk gains his new role in the community through religious experiences of ecstasy and calling.
The unfortunate reality
Black Elk decides from the content of these visions and religious experiences that his role is to be the arbiter of fate. He believes that with sincere devotion and hard work, he is being granted an opportunity to save his people as a miraculous messiah figure. Instead, he realizes that the US government is set in their ways, committed to removing Native peoples from their ancestral homelands. The unfortunate reality is a painful reminder of what dramatic irony concealed from Black Elk; he is not there to save his way of life, but rather, he seems to be a true martyr who will experience the death of his way of life. The hope is merely a tool for contrast to make his "witness" more plenary.
The entertainment motif
This story touches on a common motif which can be frequently found in minority American literature. Whether Native, Asian, Black, female, gay—whatever the case may be, there is a tendency for minority groups to be socially disadvantaged and disenfranchised, to be later resurrected to a role of entertainment. Situationally, this is ironic because gradually, Black Elk realizes that this kind of cultural celebration is exactly the opposite of his religious intentions. Instead of resurrecting a passionate way of life, he accidentally served as a kind of museum exhibit.
Failure and prophecy
In order to see this irony most clearly, compare Black Elk to a prophet from the Judeo-Christian tradition. Which of the Old Testament prophets were able to stop the downfall of Israel and Judah? Which of the prophets were able to avoid exile and decimation? None were. That is because a prophetic voice is a singular person, and Black Elk certainly qualifies here. As a prophetic voice, he feels that he failed, but ironically, by communicating his experience, he succeeds. It was never his role to single-handedly defeat the US government and save the Native way of life.
