Why did "Lift Every Voice and Sing" become the "Black National Anthem"? Attending an African American church service recently, I was introduced to the hymn Lift Every Voice and Sing.  One of my colleagues said this was the "Black National Anthem," uniquely Christian and a great solace in the fight for civil rights.

What is it that caused this song to be so closely identified with the Civil Rights Movement, and is its theology unique to a particular brand of Christianity?

Along these lines, is there a scriptural basis for this hymn?
"Lift Every Voice and Sing" was written as a poem by James Weldon Johnson for a celebration of Abraham Lincoln’s birthday in 1900. In the early 1900's, singing this song became a way for African Americans to demonstrate their patriotism and hope for the future. In calling for earth and heaven to "ring with the harmonies of Liberty," they could speak out subtly against racism and Jim Crow laws—and especially the huge number of lynchings accompanying the rise of the Ku Klux Klan at the turn of the century. In 1919, the NAACP adopted the song as "The Negro National Anthem." By the 1920s, copies of "Lift Every Voice and Sing" could be found in black, often Baptist, churches across the country.

In the 1970's, this song experienced a revival with the Civil Rights Movement.

It resonates strongly as a Christian hymn because it is a song about exodus. It is a story of a journey sanctified by faith, and protected and prospered by God.  For African Americans, the civil rights movement was their exodus story. Segregation, disenfranchisement, and racism were their Egypt, and this song was inspiration for the journey.

Bearden, Romare and Henderson, Harry. A History of African-American Artists (From 1792 to the Present), pp. 168-180, Pantheon Books (Random House), 1993, ISBN 0-394-57016-2