Truth

Why is it important that this book is truth, not fiction? Why is it important that the editor didn’t clean it up, either in terms of language or content?

This book was written to persuade people that slavery is evil and wrong. A fictional account of a slave's sufferings would be dismissed as imagination. Fiction is not fact. People could dream up numerous horrors a slave might have suffered, yet no one would believe them. The best way to reveal the truth is to tell the truth.

Again, taking the book in context of its times, it's important that the editor did not clean it up because it would become less truthful. People might suspect from the better language and grammar that it was fake, written by a better-educated person than a slave. Or they would think that all slaves had enough opportunity, somehow, to learn to write so well, and assume that slavery couldn't be all that bad. As for content- the whole purpose of the book was to show the horrors of slavery and the whole experience of slavery. To cut any of it out would be to lie by omission- to present a different, untrue version of slavery.