Dawn Eden Goldstein writes:

The text of The Noonday Devil is neatly divided between two initial chapters outlining the development of theological thought on acedia and two subsequent chapters providing practical advice for combating it. Nault’s historical analysis follows a ressourcement approach that will be familiar to readers of Servais Pinckaers. He begins with an extensive treatment of acedia in Evagrius and other Desert Fathers, passing briefly through other Church Fathers and Hugh of St. Victor before commencing a chapter-length account of Thomas Aquinas’s teachings on the vice.

Acedia, Nault explains, is a concern in the Desert Fathers’ writings because it “drives the monk to leave his cell and to flee intimacy with God, so as to seek here and there some compensation for the austere way of life to which he felt called by God” (11). Nault’s analysis of Evagrius provides a core insight, one which he will revisit as the book’s focus turns from theory to praxis: acedia for Evagrius comprises two complementary dimensions, the temporal and the spatial. Temporally, the acedia sufferer feels as though “the passage of time is never ending.” This sense of ennui can affect the body, bringing about “a certain physical weakness …, accompanied by the potential for a psychological disturbance.” Spatially, the acedia sufferer has “the impression of being hemmed in, of being stifled” (30).

Before developing the implications of Evagrius’s account, Nault switches gears for his Thomistic analysis. Thomas follows Gregory the Great in identifying acedia as “sorrow for spiritual good.” “And yet,” Nault adds, “in an altogether new insight, he describes it as the first sin against the joy that springs from charity. He makes it the sin against the gaudium de caritate” (62).

The remedy for acedia is, therefore, that which will restore charity in the sufferer’s soul. Nault, by means of a remarkably concise (and unmistakably Pinckaersian) account of the outlines of Aquinas’s moral theology—the exitus-reditus structure of the Summa, the nature of virtue as a habitus, true vs. false freedom, and the ultimate goal of beatitude—identifies that remedy as nothing less than the Incarnation: “Christ restores to us the hope of being able to participate fully in the divine life” (86). …

If you take the two definitions of acedia that we mentioned in the writings of St. Thomas Aquinas, the “sadness about spiritual good” and “disgust with action,” and you abandon the unified concept of Christian action in which the Holy Spirit and Christ are at the very heart of this action, you will see that sadness becomes [characterized as] “melancholy” and the paralysis of action becomes “sloth.” (105)

At the start of the second half of The Noonday Devil, Nault notes that he is not so interested in “[analyzing] the causes of the rather disillusioned outlook of our modern world” as in proposing “the current relevance of acedia in the life of a Christian” (107‒08, emphasis in original). By understanding the nature of acedia, the Christian may guard against temptations toward nihilism and despair.

“Modernity,” writes Brian Rottkamp, “tends to blur the difference between spending time in a way that elevates the individual and society and a way which is unproductive and/or harmful.”