The Irony of Turner's Failure
Turner's uprising is not successful. Although he always believed that he was destined for greatness, he fails to accomplish the final goal. He leads the rebellion, but it doesn't last. In the end, Turner believes he's won and fulfilled his life's purpose, but he still fails.
The Irony of Nurture
The glaring question of this text is whether or not Turner was gifted from a young age. His parents raised him to think he was exceptional, an idea which was quickly reinforced by special opportunities to be educated by his masters. They saw him as a threat because of the way the other slaves treated him. It's more likely that he became a great leader among the slaves because he was better educated and well respected thanks to his upbringing. His parents doubtless set him up to become great simply by telling him that he would be. It's their fault.
The Irony of Education
Similar to his parents' influence on his success as a leader, Turner owes much of his influence to his education. The other slaves didn't even know how to read and write, so they implicitly trusted Turner thanks to his superior knowledge. Yet again, it's difficult to ascertain whether Turner was smarter than his peers or if he simply had learned more.
The Irony of Massacre
At the start of the uprising, Turner shows no hints that he intends to kill every white person he finds. His fellow slaves believe they are fighting for freedom, killing as necessary to ensure freedom. Turner quickly turns the tides, however, when he starts murdering everyone without remorse. Rapidly the frenzy spreads until the event has become a full-blown massacre.
The Irony of Vengeance
Turner is out for blood. He wants to repay every wrong ever done him as a slave with precision. Unfortunately his cause is doomed from the start. He doesn't have a large enough army to be successful, so his vengeance is also his death sentence. He hurts himself arguably more than he avenges any wrongdoing of his masters.