The Afterthought of W. E. B. Du Bois’s The Souls of Black Folk is a very short (98 words) epilogue to the book. The Afterthought has meaning on at least two levels.
First, the Afterthought is a closing request, just as the Forethought was an opening request. In the Forethought, Du Bois asked his readers to
receive my little book in all charity, studying my words with me.
He is asking the people who read the book to be kind as they read and to think deeply about what they are reading. He is asking them not to dismiss what they read out of hand. In the Afterthought, Du Bois returns to this idea. He asks the readers to take the message of the book out and use it in the real world. He hopes that from their reading will come
vigor of thought and thoughtful deed to reap the harvest wonderful.
In short, what Du Bois is doing here is saying to the reader “now that you have read my book, please think about it carefully and act on those thoughts so that we can improve our world.” In that sense, the Afterthought is something of a call to action to the person who has read the entire book.
Second, though, the Afterthought is something of a challenge. He is implicitly confronting and challenging his white readership. He addresses them as if they were gods, saying “Hear my cry, O God the Reader.” By doing this, he is reminding them that they have a great deal of power over the African Americans of his time. At the same time, however, he is confronting them with the inequities of the world that they have made. He calls their time in history
this drear day when human brotherhood is mockery and a snare.
By saying this, he criticizes the world that the white “gods” have made. He indicts the white people, saying
Let the ears of a guilty people tingle with truth.
Here, he is telling the white readers that they are guilty of creating an unjust world and that they need to hear the truth about that world. In other words, he is feigning humility, calling the white readers gods, in order to challenge them to face up to the injustice of the world that they have created.
In these ways, the Afterthought of The Souls of Black Folk is both a call to action, urging readers to use the message of the book to improve the world, and a way of confronting white readers, pushing them to acknowledge that they have used their powers to create an unjust world.