In the Gettysburg Adress, what does Lincoln say about the living and why?
The ability to use the memorial of those who died in Gettysburg is part of the power of Lincoln's address. Through the invocation of the living, Lincoln is able to transform the notion of the Civil War. In expressing the sorrow of loss at those who died on the battlefield, Lincoln is able to make it a moral and political imperative that the living should not permit the dead to have died in vain and ensure that the work that goes on is done so as testament to those who "perished from this earth." The idea of being able to do this involves seeing the Civil War, according to Lincoln, as a battle that is not about slavery, but actually about the political reality and moral structure of our government. In this light, Lincoln asserts that the living have an obligation to fight the Civil War because it is critical that they recognize and honor the sacrifices of those who have died.
What Lincoln says about the living is that they need to go ahead with the work of making America a better place. They need to finish up the work that was started by the people who died on this battlefield. What they have to do is make sure that democracy will never die out.
As for why they need to do this, it is because, Lincoln says, they need to make sure that the people who died in this battle did not die in vain. The living need to make sure the sacrifice of the dead had a purpose.