Final answer:
The Gettysburg Address's theme is the preservation of the nation's founding principles of freedom, democracy, and equality.
Step-by-step explanation:
The theme, or underlying message, of the Gettysburg Address is that the ideals such as freedom, democracy, and equality, upon which the nation was created, are worth preserving. Abraham Lincoln's speech during the dedication of the Soldiers' National Cemetery at Gettysburg emphasized the ongoing effort to maintain the Union and the principles of liberty and equality.
The address underscored the sacrifices made by soldiers and the importance of ensuring that these sacrifices were not in vain, as well as to reaffirm commitment to the nation's foundational principles—government 'of the people, by the people, for the people'—and to the belief that the nation must have a 'new birth of freedom' to guarantee the survival of these ideals.