Why didn't Calpurnia's church have hymm books?

Calpurnia's church didn't have hymn books because most of the congregation could not read.

“Yeah, it’s called linin‘. They’ve done it that way as long as I can remember.”
Jem said it looked like they could save the collection money for a year and get some hymn-books.
Calpurnia laughed. “Wouldn’t do any good,” she said. “They can’t read.”