In the final pages of The Interpretation of Dreams, Freud surveys the terrain he's covered and takes advantage of this last opportunity to compare his theory of dreaming to those that have come before it.
Freud also uses this opportunity to plug his methodology one more time, and he outlines the contributions that his methods can make to contemporary psychological practice. Ever humble, he also admits that there are some realms of knowledge that are beyond his reach—for instance, ethics.
Freud's final paragraph reiterates his position that dreams can tell us nothing about the future. In fact, he says that "[t]here is of course no question of that" (7.7.18). Readers should be taking this for granted by now (if they hadn't been before), so why does he raise this issue one last time?
By lightheartedly noting that dreams can't predict the future, Freud gives himself an opening to drive home one of the most fundamental points that he makes throughout The Interpretation of Dreams, which is that dreams "give us knowledge of the past" (7.7.18). Not only do they teach us about our individual infancies and childhoods, but, according to Freud, they can also teach us about humanity's archaic past. That's not nothing. In fact, that's huge.
So, by ending the book on this note, Freud leaves his readers with a sense of the sheer potential of his methods. The implication is that by following Freud's lead and engaging in his method of interpreting dreams, psychoanalysts, psychologists, medical practitioners, researchers, and even cultural historians will break paths into exciting new territory.
To paraphrase Buzz Lightyear: the interpretation of dreams will bring us to infinity, and beyond.