This thorough piece of research is of great interest not only to historians but also those interested in the evolution of doctrines and religious practices. I will review this book in the latter's perspective.
A preliminary chapter gives background information about religious life in Brittany, in Western France. One main characteristic was the centrality of purgatory and the number of Masses offered for the dead. Thus in the provincial town of Nantes, there were twelve parishes and six convents (p. 25); in one of these parishes in about 1545 many private Masses were offered in side chapels besides the Mass at the main altar, namely "at least three on Mondays, two on Wednesdays, four or five on Fridays, Saturdays and Sundays," that is, about twenty Masses per week, mainly for the souls in purgatory (p. 31). Besides Masses in parishes, there were also many requiem services in convents which were ubiquitous: 123 new convents were founded in Brittany between 1580 and 1680, in addition to the existing ones (p. 23). The clergy was plethoric: about one priest per 100 inhabitants (p. 19).
Chapter 3 surveys the publications of the period, most of which described the doctrine and practice of satisfaction. God forgives all sins at baptism, but "Christians who offended after baptism had to make amends through penitence and temporal penalties. This is satisfaction. If satisfaction is not completed during a person's lifetime, the debt remained after life" to be paid in purgatory ( p 51). One could shorten one's stay in purgatory "through the application of the sacrifice of the mass" and indulgences. This doctrine was upheld by the Council of Trent in its Session VI in 1547.
The most interesting chapter from a sociological perspective is the one on "perpetual foundations for intercession" (chapter 4). Anyone could create a foundation to have Masses celebrated forever through the transfer of money or property. An easy way was through one's will. About one in five testators requested a perpetual foundation; the average number of masses requested was about 100 (p. 90). These masses could be divided between several altars, churches and convents. Moreover, there was a choice, besides the requiem Mass at the funeral, of an octave Mass, or a Mass once month, or thirty Masses over 30 days, or annual Masses forever. In one diocese there were already 1,238 foundations in existence by 1550, or 448 in the city of Nantes mentioned above. The author provides a graph showing the increase of foundations over time: between 1550 and 1650 foundations increased from about 20 to about 70 new ones every year, before collapsing after 1700. Surprisingly, "the majority of foundations were of people of modest fortunes" (p. 96). It seems that most people invested in foundations for the afterlife, and as a consequence the church grew richer, with more priests and convents needed to satisfy the demand. As we know, these foundations (called chanceries in England) were expropriated by Henry VIII in 1545, and disappeared in France in the turmoil of the French Revolution.