Spirituals are religious folk songs that originated with
blacks in the American South. Many of the lyrics are based on
Exodus, and call upon God to free the slaves, end hard
labor, and carry the blacks to a better land. Spirituals frequently
contain a chorus that's repeated after every line (such as "Let my people
go!" in Go Down Moses or "Comin' for to carry me home" in Swing Low
Sweet Chariot). This structure allows everyone to participate in the
song, including illiterates and people who didn't yet know
the lyrics. Musically, spirituals tend sound like dirges, but
they're strangely uplifting dirges at that--they always contain a glimmer
of hope in their descriptions of pain and suffering.
Some authors note that slaves used spirituals to send information to
other slaves or Underground Railroad members--Swing Low Sweet Chariot
meant that the slave was willing to take a chance at freedom, for example,
while O Canaan signified an escape to Canada.