"The Course of Human Events."

In 1972 the National Endowment for the Humanities founded the Jefferson Lecture in the Humanities lecture series, which the NEH describes as "the highest honor the federal government confers for distinguished intellectual achievement in the humanities." David McCullough won the honor of being the 2003 Jefferson lecturer and gave a great speech on the arc of history, the text of which can be found here.

McCullough's general point:
"The truth of history is the objective always. But the truth isn't just the facts. You can have all the facts imaginable and miss the truth, just as you can have facts missing or some wrong, and reach the larger truth."

Random note about McCullough: He still uses a 1940s typewriter and writes only in a small shed/studio behind his house on Martha's Vineyard (seen in the above picture).