Diego Lucci offers a well–researched study of Locke's religious views and beliefs, with a focus on his late works, in particular on The reasonableness of Christianity. Locke's engagement with Scripture and his Scripture-based soteriology are at the heart of this study. Locke's insistence on fundamentals, an echo of Melanchthon's adiaphora discussion, has a highly individualistic tenor. Despite Lucci's efforts to argue the opposite, the uniqueness of ‘Locke's Christianity’ (p. 211) suggests that he was at the margins of the theological debates. At the same time, he took care ‘to avoid making statements that could be perceived as heretical’ (p. 172). Detailed analysis of his manuscripts and correspondence serve as a bedrock for contextualising Locke's religious thought.

Le Clerc, Limborch and Newton were particularly influential in shaping Locke's views on the Trinity. This issue provoked deep conflicts among clergymen in the Church of England itself, causing ‘deep embarrassment to the ecclesiastical and political authorities’ (p. 140). Locke held anti–Trinitarian views that were also inspired by Socinian and Arian influences. However, as Lucci points out, despite Locke's close engagement with this controversy – confirmed by several manuscript notes (cf. p. 144) – he remained publicly silent about his anti-Trinitarian convictions. This silence was quite telling. Locke's ‘Reasonableness completely disregarded the Trinitarian doctrine in the midst of the Trinitarian controversy of the late seventeenth century’ (p.155). Notwithstanding his manifest interest in and study of one of the most sophisticated and protracted theological disputes, Locke remained at the fringes and shied away from open involvement. Presumably, a more outspoken intervention from his side would not have changed much of this debate, though Lucci does not propose to speculate along these lines. He contents himself with detailing Locke's privately-held position on this matter, and on the well-known criticism his Reasonableness attracted from divines like John Edwards or the bishop of Worcester, Edward Stillingfleet (cf. pp. 159ff.).

Lucci's competent discussion and detailed description of Locke's concerns regarding some of the most complex theological debates seems to suggest, at least implicitly, that he was at the heart of these debates. Even regarding the controversy about the Trinity, Lucci appears to imply this. However, was Locke really such an important participant in the religious debates of his time as Lucci insinuates? He was rather significant for shaping the epistemology of his time, which in turn had an influence on the way theological and philosophical investigations were conducted. Lucci's book touches on another question that is even more debatable: What was the relevance and use of religion in Locke's political writings? Lucci repeatedly refers to this crucial issue, and even claims towards the end of his study that Locke developed a ‘political theology’ (p. 205). Yet his book does not develop a sustained analysis of this matter. Lucci is certainly right in asserting that ‘Locke's natural law theory … is grounded in both natural and biblical theology’ (pp. 10, 86). But what were the consequences of such a theological grounding of his political thought? What was the role of religion in this context? Or, put differently, did Locke see a political role for religion?

While these questions are not his book's main concern, Lucci nevertheless raises expectations that the reader might find answers to them. Although his analysis brings him tantalisingly close to addressing questions about religion and politics, we learn precious little about Locke's ways of ‘drawing on scripture in his political thought’ (p. 86). According to Lucci, Locke was ‘in general agreement with the ideas of seventeenth-century natural law theorists such as Hugo Grotius and, above all, Samuel Pufendorf’ (p. 86). Locke may have agreed with many of Grotius’ positions, but it is misleading to make such an explicit claim for the relationship between Locke and Pufendorf. The only shared ground – not touched upon by Lucci – between the two men, in particular after Louis xiv's revocation in 1685 of the edict of Nantes, is their concern to defend European Protestantism against what they perceived as a Catholic onslaught. There are fundamental differences between the two in their understandings of the state of nature, the right to punish in the state of nature, the notion of property and the concept of sovereignty. Pufendorf's concept of the state as a moral person is also much more complex than Lucci believes it to be, simply asserting that it ‘is the sum of the individuals’ wills’ (p. 87). Most importantly, Locke's claim that ‘the people may, as a last resort, instigate a revolution against the government when the latter acts against the citizens’ civil interests’ (p. 88) is clearly at odds with Pufendorf's views. His theory of the state and sovereignty could not be upheld if the people were granted the competence to make such a decision. In the political realm, for Pufendorf, the essential question was ‘quis iudicabit’: who decides? Pufendorf's answer could not be mistaken: only the sovereign was in a position to do so.

The same question ensues in the religious realm. Ever since Melanchthon, the insistence on sola scriptura posed precisely this essential question of ‘quis iudicabit’. Neither Locke nor Lucci see reference to Scripture as the deciding factor about religious belief as a problem (cf. pp. 69f.). However, confessional strife arose out of conflicting views on how to interpret Scriptures and from competing confessional claims about who had the ultimate authority to make final decisions in these matters. It is here that Locke is least convincing, not just because he simply denied the legitimacy of Catholics’ claims, but also because he conveniently assumed that ‘the faithful ought to study Scripture to the best of their abilities in order to live the Christian life and pursue salvation’ (p. 69). Lucci glosses over such social and political shortcomings of Locke's religious doctrine. For those who are interested in these problems, this is not the book to read. For those, however, who are interested in the intricate theological debates of the seventeenth century and Locke's reaction to them, this study provides a detailed and worthwhile reading. Lucci's study demonstrates convincingly that Locke was ‘a Christian thinker’ and that ‘he employed both natural and biblical theology in his political thought, and [that] he always maintained a markedly religious conception of morality’ (p. 214). Future scholarship on Locke will have to engage with Lucci's revisionist plea to reconsider the prevalent perception of the ‘liberal’ and ‘secular’ Locke.