Duty and obligation are the cornerstones on which any military tradition is based. So it makes sense that, during this time of war, President Lincoln invoked these sentiments to stir the crowd to action.
His words made it clear that the burden of winning was a shared one—one that he carried along with every American fighting for a Union victory. In these tough times, when people looked to be consoled and for meaning in all the bloodshed, a rigid sense of duty helped bring the nation together.
More important than stronger forces, better technology, or a superior sense of style, motivating people is necessary for countries to win wars.
America in the 19th century was a society built around honor. So when called to action by President Lincoln, the response was overwhelming.
If you've ever been to an international sporting event and heard the deafening "U.S.A.! U.S.A.!" chants, you understand the power of patriotism.
And so did Lincoln.
Patriotism was especially powerful during the Civil War, which pitted brother against brother. Allegiance to one's country became the strongest bond of all. So President Lincoln didn't shy away from a bit of patriotic zeal in the Gettysburg Address.
He glossed over some of the more problematic aspects of American society in favor of a depiction of the United States as a nation of the people based on principles such as equality. While this was truer at the end of the Civil War than before it, there was still a lot of growing to do.
Patriotism is a powerful but dangerous tool in any speaker's arsenal. Defining oneself by this kind of identity inevitably turns into an "us versus them" mentality that can be hard to overcome. These strongly held beliefs are partly why Reconstruction was such a difficult process.
When push comes to shove, it seems that loyalty to one's country can be the first thing to go. One need only ask Benedict Arnold to see how much patriotism can be worth. So while it appeals to some, it's far from the strongest of bonds.
In this speech Abe Lincoln doubled down on equality as one of the building blocks of our society. By referencing the idea that all men are created equal, in one deft move Lincoln compared the importance of the war that was then raging to the American Revolution itself, while drawing clear attention to the fact that the Emancipation Proclamation made this statement significantly more truthful.
Despite proclaiming that "all men are created equal," this line in the Declaration of Independence rang false to those who wrote it. The contrast between the meaning of the words and the institution of slavery led to the Civil War.
While it is obvious that there's a wide gulf between the statement "all men are created equal" and the situation in 1865, it can still be said that the United States displayed a pretty unrivaled amount of equality. The Bill of Rights guarantees equality in the eyes of the law, something that we occasionally take for granted even in the 21st century.