The book provides one of the few contemporary, firsthand accounts of Nazi Germany written by a Western journalist who had direct access to high-ranking Nazi officials while maintaining an outsider's perspective. Its day-by-day format captures events as they unfolded, without the benefit of hindsight, making it an invaluable primary source.

Shirer balanced his role as a professional journalist with his personal observations and moral judgments. He maintained detailed private records while navigating strict censorship, and his diary entries reflect both his attempt to remain objective and his growing personal horror at the events he witnessed.

Unlike post-war accounts or historical analyses, Berlin Diary captures the immediacy and uncertainty of the period. It shows how events appeared to contemporary observers who didn't know the ultimate outcome, providing unique insights into the atmosphere of pre-war Germany and the gradual build-up to World War II.