"Sweet Freedom's Song"

I stumbled across the phrase "sweet freedom's song" while singing "My Country 'Tis of Thee" today. Has it always been there?
I wonder. Which makes the most difference in the world, the official documents of freedom like The Declaration of Independence and The Constitution or little catch phrases like sweet freedom's song, that etch themselves deep into our hearts--phrases like "I have a dream," "In God we trust," "This land was made for you and me," "with liberty and justice for all," and ". . . of the people, by the people, and for the people?"
I know what my answer would be.