It is a quote from the words of "My Country tis of Thee;" it is "My country tis of thee, sweet land of liberty." Now, the people at the time did not feel this was the "sweet land of liberty." He picked this particular song - it is fascinating to me that he picked it, because this song is what they used in the anti-slavery movement as an outcry of the fact that this was not the "sweet land of liberty." It actually changed up the words as an outcry against the promise of the song; so the song had mixed emotion for the people in the audience, because it was a promise, but it was also something they had been singing as an outcry. 