Equiano's book is considered a quintessential example of an enslaved person's narrative because it is one of the first commercially successful accounts of an enslaved person's life from childhood to adulthood. But this genre didn't really exist yet when Equiano was writing, and it is important to note that Equiano draws on several other genres. One of these genres is spiritual autobiography. Equiano structures his narrative in part around his own religious development. He learns to read the Bible and visits many religious teachers as he attempts to understand his own relationship to Christianity. Some of the later chapters contain complex meditations on religious doctrine that seem to be modeled on other spiritual autobiographies, especially Saint Augustine's Confessions.
Equiano also describes his adventures in many corners of the world, and he includes detailed descriptions of the customs he observes in different societies. In this aspect, his book is a travel narrative. Travel narratives became especially popular in the 18th century, as the British Empire spread. Readers at home in England liked to read about the journeys explorers and colonists took to various far-off parts of the world. Not only were these narratives engrossing, but they also gave non-travelers the chance to "see" places far and wide (places that were, of course, being colonized by the British Empire).
On top of all this, Equiano's book is also an appeal to white lawmakers to abolish the slave trade. Equiano weaves all these elements of different genres into his argument in part because he knows that they will make it more effective. His readers are familiar with spiritual autobiography and with travel narratives. They have likely enjoyed reading other books in these genres and are therefore primed to enjoy Equiano's book too. Furthermore, signaling that he is familiar with both of these genres helps Equiano bolster his credibility as an intelligent British citizen who is participating fully in the same culture his readers occupy. There is an argument to be made that courting this credibility is a concession to white supremacy and colonist society, but it is also key to Equiano's success in getting the British government to examine the inhumanity of the slave trade.