Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
The Rise and Fall of the Third Reich has four—count 'em, four—epigraphs. Let's take them one by one.
Goethe
I have often felt a bitter sorrow at the thought of the German people, which is so estimable in the individual and so wretched in the generality...
—Goethe
Here, Shirer draws on Johann Wolfgang von Goethe to signal the fact that TRFTR isn't going to go easy on the millions of Germans who supported Hitler's leadership. Throughout the book, Shirer repeatedly depicts the German public of Hitler's day as being like a flock of sheep or a herd of cattle. Although the term "groupthink" wasn't current when either Goethe or Shirer was writing, this epigraph points to the mob mentality that Goethe sees as common in the German people.
Walther von Brauchitsch
Hitler was the fate of Germany and this fate could not be stayed. —Field Marshal Walther von Brauchitsch, Commander in Chief of the German Army, 1938-41
Shirer's second epigraph could be read in one of two ways.
On the one hand, Shirer himself argues in TRFTR that "without Adolf Hitler […] there almost certainly would never have been a Third Reich" (1.1.14), and he goes to some lengths to prove that the Fuehrer was an inevitable product of German history and German culture. In this sense, Field Marshal Brauchitsch's declaration that Hitler was "the fate of Germany" seems to support Shirer's own perspective.
On the other hand, throughout TRFTR Shirer also lambasts the German Army officer corps for its defeatism and fatalism, and he frequently takes the officers to task for doing so little to oppose Hitler when they had the chance. In this sense, Shirer seems to be using Field Marshal Brauchitsch's comment as a reminder of the indecision, inaction, and defeatism of the German Army officers who went along with Hitler's plans.
Hans Frank
A thousand years will pass and the guilt of Germany will not be erased. —Hans Frank, Governor General of Poland, before he was hanged at Nuremberg
Shirer tells us in his "Brief Epilogue" that Hans Frank, the Nazi Governor General of occupied Poland, was "contrite" in the end, and begged God's forgiveness for the atrocities in which he had taken part (Epilogue.6). That said, this epigraph has little to do with Frank himself. Shirer isn't trying to remind us that Frank eventually felt bad about participating in the deaths of millions: instead, he's simply offering Frank's words as a statement of basic, indisputable fact.
George Santayana
Those who do not remember the past are condemned to relive it. —George Santayana
As Ron Rosenbaum writes in his Introduction to the Fiftieth Anniversary Edition of The Rise and Fall of the Third Reich, by 1960—when Shirer's book was first published—there seemed to be "a wave of amnesia" regarding the Second World War and all that it had entailed. Rosenbaum even describes "a kind of willed forgetfulness of the horror of those years" (Introduction).
By paraphrasing philosopher George Santayana's well-known warning about the dangers of forgetting the past, Shirer uses the final epigraph to characterize TRFTR as an antidote to the kind of "willed forgetfulness" that Rosenbaum described. By educating ourselves about the past, he seems to suggest, we can help to make sure that historical horrors never happen again. (See our "Why Should I Care?" Section for more on that.)