A spiritual is an African American song, usually with a Christian religious text. Originally monophonic and a cappella, these songs are antecedents of the blues. The terms Negro spiritual, Black spiritual, and African-American spiritual are all synonyms; in the 19th century the term jubilee was more common (at least among African-Americans; whites often called them slave songs). Some musicologists call them African-American folk songs.
During slavery in the U.S., there were systematic efforts to de-Africanize the captive black workforce. Slaves were forbidden to speak their native languages, to play drums, or practice their mostly Animist and Muslim faiths. They were urged to become Christians and often forced to identify as Christians by slavemasters who often used Christianity as a tool of control.
The Moravian Music Foundation - Organization preserving and publishing the heritage of Moravian music in Colonial America. Site includes a shopping cart with sheet music, recordings, monographs and books.