What is the theme in A Distant Mirror: The Calamitous 14th Century by Barbara W. Tuchman?

Religion is a main theme in the novel, A Distant Mirror: The Calamitous 14th Century. Throughout the text, we become aware of the importance of religion during the Middle Ages, specifically, its importance in daily life, and to those in need of repentance. Negatives such as bribery by church officials is also addressed.