All roads to our America lead through Gettysburg. 150 years ago, President Lincoln arrived there around dusk and set foot on the sacred soil that, just four months earlier, had run with blood of the Civil War. Then the next morning, November 19, 1863, he stood under a clear sky—on earth since transformed from a battlefield to a burial ground—and delivered a deceptively simple speech atop Cemetery Hill that, in just a few short minutes, changed American history forever.

To this day, the Gettysburg Address continues to shape who we are as a people and as a nation. Without it, we don’t have Martin Luther King, Jr. standing on the steps of the Lincoln Memorial 100 years later saying, “I Have a Dream.” We don’t have John and Robert Kennedy taking the first tentative steps toward civil rights legislation. We don’t have, nearly 50 years after that, the election of our nation’s first black president.

Without the Gettysburg Address, we don’t have the promise of America brought to complicated, often difficult life....