I actually like the wording of this answer. Indeed, the primary rhetorical device that Douglass used was an unflichingly powerful narrative that explored slavery. He sought connection with the reader, and in doing so hoped to transform them from one who could not claim awareness or understanding of the problem of slavery to one who stood firmly against it. It is here where Douglass sought to have a "better effect" on the audience, as his primary purpose was the spiritual transformation of the reader. Douglass' style of immediacy, seeming to instantly place the reader in the condition of slavery in order to fully gauge its brutality is one where he deliberately hopes to act on the sense of conscience of the reader. Douglass knows that majority of his readers will be White, as people of color at the time did not enjoy the benefits of universal and quality education. He recognizes that in being able to fully relay the impact of slavery through a rhetoric that places the reader almost "in media res" of what slavery is, there will be an empathy and understanding that will compel the reader to conclude slavery is awful and advocate for its abolition. It is here where Douglass seeks to make the audience "better" for having read its book. There are not many works of literature whose direct purpose is to make the audience "better," to transform the spiritual level of the audience to a point where greater spiritual awakening is the direct result of reading a text. Through Douglass' rhetoric and style, though, he aims to make the audience spiritually and ethically better by reading and understanding his text.