Rob Iliffe's Priest of Nature: The Religious Worlds of Isaac Newton is a work of excellent historical scholarship. I have no significant negative critiques to offer. Therefore, I provide a summary of foundational events from Iliffe's narrative that assist in understanding the core of Newton's religious convictions.

One of the most clouded questions surrounding Isaac Newton is: how did Newton arrive at theological conclusions that, according to Iliffe, had they been widely known, would have put Newton in the company of other radical reformers? Instead of the orthodox understanding of the Trinity—One God who exists as three equal, eternal, and homoousios (same substance) persons of Father, Son, and Holy Spirit—Iliffe identifies “the hideous nature of tritheism, and the radically subordinate status of Jesus Christ relative to the Father” as the “dominant doctrinal points in Newton's theology” (134). Iliffe observes that from the mid-1670s, as part of the recently reinstated Divinity Act, all masters of arts students were required to “propose two questions on theological topics and to read a thesis on the first” (133). As a part of this process, in February 1677, Newton opposed the Socinian view that God did not know future events that God did not foreordain. Perhaps Newton found some aspects of Socinian belief attractive, such as the strong emphasis on scripture and the claim that Christianity, at its core, is a simple religion that all rational people can understand. Whatever the case, once Newton had passed the Divinity Act, he turned his attention to church history and to the Bible—especially apocalyptic texts. Iliffe poetically says, “During this hermitage he had a physical presence in his seventeenth-century Trinity rooms, but effectively lived out much of his life in the fourth century, when (as he saw it) pristine Christianity was corrupted by the importation of the despicable beliefs and practices that would later constitute the core of Roman Catholic faith, chief of which was the doctrine of the Trinity” (133).

What exactly did Newton discover in his Cambridge University Trinity rooms about the Trinity? In chapter 5, “Abominable Men,” Iliffe provides answers. As the result of much independent research—it is unlikely that Newton was influenced by other heterodox trinitarians, such as John Locke, John Bidle, Paul Best, Christopher Sand, or Thomas Hobbes—Newton decided that the Council of Nicaea did label the relationship of the Son to the Father with homoousios. However, the exact meaning of the word was not clear, and the decision itself was not unanimous.

Nonetheless, Newton was persuaded that the term did not mean that the Father and Son are of the exact same substance—especially since homoousios had been condemned in 269 CE due to Paul of Samosata's manner of usage. Rather, the generally agreed upon meaning from the Council of Nicaea was that the Father and the Son were of a similar substance. Where did things go awry? The central figure to Newton's reconstruction of the corruption of Christianity is Athanasius of Alexandria—bishop of the church in Alexandria, Egypt, from 328 to 373 and a deacon when the Council of Nicaea convened in 325. So great was Newton's disdain for Athanasius that “his position is better described as anti-Athanasian rather than pro-Arian.” And it is his “explicit and relentless hostility to Athanasius and his core beliefs that marks Newton out as so radical” (145). Thus, Newton believed that when Julian became Roman emperor in 361, Athanasius returned from exile in Egypt and introduced another misconception, in addition to homoousios meaning same substance, of the Trinity that understood each person of the Trinity as a separate hypostasis. Now Athanasius and his co-religionists began to rewrite the scriptures as well as documents from the Council of Nicaea and pre-Nicaean patristic texts in such a way that favored their interpretation of what transpired at Nicaea (154).

Iliffe narrates the fascinating account of Newton's letter to John Locke, which included Newton's “Historical Account of Two Notable Corruptions in Scripture.” In this piece, Newton puts forth evidence that leads him to believe that the Johannine Comma—1 John 5:7 in the Kings James Version, “For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one”—had been inserted into the text by later scribes. This verse was originally found in the margins of copies of 1 John, and Newton believed it was a scribal interpretation of 1 John 5:8 in the Kings James Version: “And there are three that bear witness in earth, the Spirit, and the water, and the blood: and these three agree in one.” Newton also thought that 1 Timothy 3:16 from the King James was inauthentic: “And without controversy great is the mystery of godliness: God was manifest in the flesh.” Newton observed, as others before him, that the word “God” was not in the earliest Greek manuscripts, nor was this reading found in Jerome's Vulgate. Rather, the authentic reading is, “Great is the mystery of godliness which was manifested in the flesh.” Newton thus provided additional credible arguments against the authenticity of the two biblical texts that provided the strongest proof for the orthodox understanding of the Trinity.

What is most interesting, however, is that Newton sent his “Historical Account of Two Notable Corruptions in Scripture” to Locke with the request that Locke have this work translated into French and published sans Newton's name. However, “the whole translation process took so long that he came to his senses and suppressed them” (370). Newton considered publishing this work once more. In 1709, Newton asked Hopton Haynes to translate the discussion of 1 John 5:7 into Latin. However, “this was an even less propitious time to publish the work and it too was held back” (370). It appears that Newton's preference for private correspondence won out. As Iliffe notes, “It was after all, merely, a letter to a friend” (389).

Iliffe's 522-page tome is devoted not to Newton's mathematical or philosophical work (though there is significant discussion of these areas as well; thus the title Priest of Nature) but to Newton's heterodox understanding of a foundational Christian belief: the Trinity. Iliffe's work proves his own observation that Newton's “extensive writings on the Trinitarian corruption of Christianity are among the most daring works of any writer in the early modern period” (11). Furthermore, Iliffe contends that Newton's heretical writings are on par with those of Richard Baxter and Nehemiah Wallington, and they would demand careful study even if they were not written by the same person who penned the Principia. Indeed!