Who is Mr. Shan from Gladys Aylward: The Little Woman and what is their importance?

Mr. Shan is a hardened criminal, whi is incarcerated in a local Chinese prison for murder. When Gladys preaches at the prison, Shan responds by cursing and spitting at her. When Gladys directly appeals to him by touching his shoulder, however, Mr. Shan eventually come around and become a Christian. After his conversion, the majority of the prison population follows suit.