You don't have to be a polished singer to join in with Sacred Harp singing. While it doesn't hurt to be able to read standard music notation, many singers learn by ear. We sing from The Sacred Harp, a book first published in 1844, a collection of Early American Christian hymns and anthems, written explicitly for the "Singing Schools" of the era. We always have loaner copies available at all of our meetings (or "singings" as they are referred to).
While many of the songs have explicit Christian references, our group is non-denominational. Singers take from the singing whatever whatever spiritual content fits for them.