Why are the blacks linin their hymns in To Kill a Mockingbird?

The church does not have enough money to purchase hymn books and also, only four people in the church knows how to read so it would be useless to even buy hymn books. Zeebo and Calpurnia(son and mother) are two of the four that knows how to read and Zeebo sings the hymns while the other black people just follow behind him. Hoped that helped. (: