Please keep in mind that the full title of this book is Praying for Sheetrock: A Work of Nonfiction. As such, this book shows the continuation of the Civil Rights Movement in McIntosh, Georgia.
Originally, it seems that this small county in Georgia just ignored the rest of the country in the sixties in regards to the Civil Rights Movement. The "law" represented by the sheriff (Tom Poppell) was still the main source of justice: improper and unjust justice. In fact, it took Thurnell Alston (an unemployed and uneducated black man) moving to the area to turn things around.
The irony is that before the 1970s, the white and black populations of McIntosh County seemed to get along, but were really completely immersed in racial inequality. The black people were still the servants, the white people were still the masters, and the sheriff still ruled them all. Thurnell Alston, who used to be a boilermaker in his younger life, is appalled when he moves to McIntosh. Thurnell Alston, in his uneducated wisdom, hires lawyers to help bring the town closer to equality and the rest of the book is the county's response which is "both poetic and sad" according to eNotes.
In conclusion, it is important to note that the title is actually a God-reference. Because the community (in the throes of racism) was simply dependent of economic miracles to get back, they were always waiting for the "Sheetrock-Deliverer." The irony is that God eventually works His will through Thurnell Alston.