Beyond the unifying symmetry of the numbers, what binds and animates the new “Changing America: The Emancipation Proclamation, 1863, and the March on Washington, 1963” exhibit at the Smithsonian’s Museum of African American History and Culture gallery is the great press of American people toward freedom.

It is a constant, relentless force before, during and after these iconic moments in history, with a sweep that is nationally momentous and deeply personal. It winds between the artifacts, giving them weight and suasion.

The gallery, inside the American History Museum, divides into two sides and organizes around a quote from labor and civil rights leader A. Philip Randolph: “Freedom is never given, it is won.”...