Here is a piece that got forwarded to me written by President Obama:

Three years before he entered Gardner’s studio, Lincoln termed the United States, in one of his early messages to Congress, “the last best hope of earth.” Considering that our fragile Union was not 100 years old and stood a good chance of dissolving, it was an improbable thing to say. But Lincoln saw beyond the bloodshed and division. He saw us not only as we were, but as we might be. And he calls on us through the ages to commit ourselves to the unfinished work he so nobly advanced—the work of perfecting our Union.

For more: http://www.theatlantic.com/magazine/archive/1969/12/perfecting-our-union/8832/