Since 1988, when Cambridge University Press published Biancamaria Fontana's translation of Constant's Principles of Politics and On the Spirit of Conquest and Usurpation, along with his famous speech on the liberty of the moderns and the ancients, there has been a remarkable revival of interest in the writings of Benjamin Constant in both the United States and the United Kingdom. Today, he is recognized as one of the most original and important of modern liberal thinkers, even if his political shifts have made him for some the paradigmatic figure of political opportunism. In spite of this revival, Constant's monumental five-volume De la religion (1824–1831) and his other writings on religion are often missing from the interpretations of his liberal doctrine. This phenomenon is all the more surprising because Constant himself called On Religion “the only consolation” of his life and believed that he was “destined by nature” to write that book.

Helena Rosenblatt, a historian of modern French thought who previously worked on Rousseau and Geneva and has recently edited The Cambridge Companion to Constant (2009), has written a learned book that attempts to redress this regrettable oversight. Her interpretation of Constant is the first published book in English that integrates Constant's views on religion and his ideas on politics. Rosenblatt argues that understanding Constant's religious ideas and his Protestantism is indispensable to any student of his political writings. Failing to address his religious concerns, we get a distorted and truncated image of Constant's liberalism, and thus miss the moral concerns that pervaded his liberalism.

Tightly organized around a few central themes and drawing upon a wide array of primary and secondary sources, Rosenblatt's book has an ambitious scope and agenda. It combines textual analysis with a close interpretation of the relevant intellectual and historical context. It recounts Benjamin Constant's intellectual trajectory by offering an overview of all his major political works. Brief discussions of select writings by authors with whom Constant had a sustained intellectual dialogue (among others, Madame de Staël and Necker) are also included. Thus, we get to follow Constant from his education in Germany and Scotland, his encounter with the writings of the philosophes, and his political involvement during the Directory, to his famous opposition to Napoleon. Constant's short collaboration with the Emperor during the Hundred Days in 1815 and his parliamentary career during the Restoration follow. A special chapter discusses Constant's religious views and his masterpiece, De la religion, followed by a final assessment of Constant's legacy.

Rosenblatt does a particularly good job tracing the evolution of Constant's religious ideas and relating them to the larger intellectual context from which they emerged. His initial opposition to Christianity developed partly under the influence of Helvétius and affected his perspective on the French Revolution. As late as June 1794, Constant held radical views and believed that “to occupy the middle ground is to take up a worthless position” (25). Constant's decisive meeting with the German theologian Jakob Mauvillon (1743–1794), an admirer of Kant, and with the milieu of the German Aufklärer, caused a fundamental shift in his views on religion. An important manuscript, “L'Esprit des religions,” analyzed by Rosenblatt (29ff), demonstrates this shift. Influenced by the idea of a perfectible Christianity and the concept of “progressive revelation” (rendered famous by Lessing), Constant came to believe that revelation, far from being timeless, can actually march along with the Enlightenment. Rosenblatt further emphasizes the centrality of the idea of private judgment to Constant's thought (130–34). From 1806 when Constant introduced the term “private judgment” into his political writings, he sought to articulate an ambitious moral vision, indebted to a Protestant way of thinking, that stressed the right and duty of individuals to improve themselves through reason. This decisive moment in Constant's evolution, Rosenblatt argues, is illustrated by book 8 of the 1806 edition of The Principles of Politics, which analyzes the proper role of government with regard to religion.

Starting from this moral vision, Rosenblatt argues, we can develop an understanding of Constant's views on religion and his theory of liberty as a means of self-development. Although Constant believed that religion serves for the creation of an elevated morality, his turn to religion never ushered in a proper conversion and did not lead him to embrace a specific religious doctrine. To assume that Constant suddenly discovered faith and became a true believer would be an overstatement. In fact, as Rosenblatt points out, the religious views that he later embraced in the two versions of his Principles of Politics (1806; 1815) and On Religion were far from conventional. His unorthodox ideas on religion met with the skepticism of devout believers and atheists alike. Constant's critics accused him of espousing a purely sentimental and individualist form of religion, and for drawing a pernicious distinction between religious sentiment and religious forms. (According to Rosenblatt, Constant retained this distinction after a meeting with the German poet Wieland in 1804.) Many of Constant's critics feared that once the principle of authority in religion is denied, there would be no principle of authority left in the realm of politics and anarchy would follow.

The Catholics and the ultras were taken aback by the fact that Constant regarded religion as a sentiment; furthermore, the central figure of Christ was conspicuously absent from his theory. For Constant, Rosenblatt points out, what mattered above all in religion were the sentiments of the sublime, the pure emotions and uplifting feelings that were not confined by any superannuated form and could thus dispense with any doctrinal content. By attacking the concept of self-interest as an insufficient basis of a free society, Constant was also bound to clash with the apostles of a new form of liberalism and the defenders of industrialism, for whom the principle of self-interest was sacrosanct. In Constant's view, the highest vocation of man is to instruct himself and to enlighten himself (228), which could not happen if he relied only on self-interest.

If Constant's religious ideas were unconventional, they were certainly much more than an expression of an idiosyncratic mind. Constant sincerely believed that life would be empty without a religious dimension. That Constant's religious views had a strong and intimate link with his political ideas is attested by his own words, placed at the beginning of his last book, Mélanges de littérature et de politique (1829) and quoted by Rosenblatt. “For forty years,” Constant wrote, “I have defended the same principle, liberty in everything, in religion, in philosophy, in literature, in politics: and by liberty I mean the triumph of individuality.” The great merit of Helena Rosenblatt's erudite and insightful book is that it sheds fresh light on how Constant achieved his goal and how he remained faithful to it to the very end of his agitated and controversial life.