The answer to my mystery song quiz is "Lift Every Voice and Sing" (LSB 964). The author is writer and professor James Weldon Johnson.
Check out your hymnal and see if you can -- without coming to it with preconceived ideas -- find the gospel in this hymn. Or the law preached lawfully. I can't.
Here's some information on Lift Every Voice, from Wikipedia:
"Lift Every Voice and Sing — often called "The Negro National Anthem" — was written as a poem by James Weldon Johnson (1871-1938) and then set to music by his brother John Rosamond Johnson (1873-1954) in 1900. It was first performed in public in the hometown of Jacksonville, Florida as part of a celebration of Lincoln's Birthday on February 12, 1900 by a choir of 500 schoolchildren at the segregated Stanton School, where James Weldon Johnson was principal.
Singing this song quickly 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 churches across the country, often pasted into the hymnals.
During and after the American Civil Rights Movement, the song experienced a rebirth, and by the 1970's was often sung immediately after The Star Spangled Banner at public events and performances across the United States where the event had a significant African-American population.
In 1990, singer Melba Moore released a modern rendition of the song, which she recorded along with others including R&B artists Anita Baker, Stephanie Mills, Dionne Warwick, Bobby Brown, Stevie Wonder, Jeffrey Osborne, and Howard Hewett; and gospel artists BeBe and CeCe Winans, Take 6, and The Clark Sisters. Partly because of the success of this recording, Lift Ev'ry Voice and Sing was entered into the Congressional Record as the official African American National Hymn."
All of which is fine as is. But what's this song doing in the Lutheran Service Book? I'll put forth my guess tomorrow.