R.C. Sproul's The Holiness of God (1985) is one of the most widely influential works of popular Reformed theology produced in the twentieth century and a book that many readers credit - more than any other - with drawing them into the Calvinist theological revival that transformed American evangelical Christianity from the 1980s onward.
Sproul was a Pittsburgh-born theologian and pastor whose academic training was rigorous (Free University of Amsterdam, under G.C. Berkouwer) and whose gift was making that rigor accessible to non-specialists. The Holiness of God is the fullest expression of his conviction that contemporary American Christianity suffered from a fundamental impoverishment of its understanding of God - an impoverishment with cascading consequences for its theology of sin, grace, and salvation.
The book opens with Isaiah 6's vision of the Holy God: 'Holy, holy, holy is the LORD of hosts; the whole earth is full of his glory' (Isaiah 6:3). Sproul observes that the threefold repetition - unique in scripture - is the Hebrew superlative of the superlative: not merely 'very holy' but 'holy beyond all comparison, utterly set apart.' The seraphim cover their faces and feet in the divine presence; the prophet, 'a man of unclean lips,' cries out that he is undone. This is not the comfortable God of therapeutic spirituality but the God who is a consuming fire (Hebrews 12:29).
Sproul's argument proceeds through the development of the concept of holiness from its root meaning - qadosh, set apart, other, different - through the Exodus narratives (Exodus 3:5, 'Take off your sandals, for the place where you are standing is holy ground') to the New Testament. Holiness is not primarily a moral category but an ontological one: God is holy because he is what he is, absolutely and uniquely, with no admixture of limitation, contingency, or sin. The moral demands of holiness flow from this ontological reality, not the reverse.
Romans 1:18 - 'For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who by their unrighteousness suppress the truth' - grounds Sproul's argument that the contemporary tendency to emphasize God's love while suppressing his holiness and wrath is not theological sensitivity but theological distortion. A God who is not angry at sin is a God who does not take either righteousness or sinners seriously. The 'wrath' of God is not an irrational emotional reaction but the settled opposition of absolute holiness to everything that contradicts it.
Hebrews 12:29 - 'for our God is a consuming fire' - is the New Testament text that carries the full weight of the Sinai tradition into the Christian dispensation. The God of the New Testament is not a gentler version of the Old Testament deity; he is the same holy God, now met in the person of Jesus Christ, whose cross is simultaneously the most severe expression of divine wrath against sin and the most complete expression of divine love for sinners.
The book's most powerful chapter deals with the 'strange fire' of Nadab and Abihu (Leviticus 10), the sons of Aaron who offered unauthorized incense and were consumed by fire from the LORD's presence. Sproul uses this disturbing episode - deeply offensive to modern sensibilities - to argue that the casual familiarity with which contemporary Christians approach God reflects a failure to understand who God actually is. The holy God of Leviticus is not a different God from the God of John 3:16; he is the same God, and the cross is comprehensible only against the background of his absolute holiness.
The book became a catalyst for what historians have called the 'Young, Restless, Reformed' movement of the late 1990s and 2000s - a wave of young evangelicals, disillusioned with contemporary megachurch Christianity, who found in Reformed theology's emphasis on divine sovereignty and holiness a more intellectually serious and emotionally honest faith. Sproul's work, alongside John Piper's Desiring God (1986) and Wayne Grudem's Systematic Theology (1994), defined the theological culture of this movement. The Holiness of God remains one of the most recommended books in Reformed evangelical circles and has sold several million copies.
Sproul's personal story of encountering Isaiah 6 and being undone by it - sitting in his study, reading the vision of the seraphim and the terrifying holiness of the Lord of Hosts, and finding that the passage broke through the academic familiarity that theological education can produce - grounds the book in lived experience as well as theological argument. He is not describing a concept but reporting an encounter, and that difference in register is what distinguishes The Holiness of God from more purely academic treatments of the divine attributes. The book asks its reader to be willing to be undone by what the text describes, and that willingness, Sproul argues, is the beginning of genuine theological understanding.
The Holiness of God has sold over a million copies and remains the best-selling work of Reformed systematic theology for popular audiences since Packer's Knowing God (1973). Its influence on the Reformed resurgence of the 1980s and 1990s - the movement associated with John Piper, John MacArthur, and the Desiring God conference - was foundational: it gave a generation of younger evangelicals who were hungry for theological seriousness a readable account of the God whose holiness makes grace surprising rather than expected. That combination of accessibility and depth has kept the book in print for four decades and ensures that it will continue to be read as long as there are Christians who want to be confronted, rather than merely comforted, by the character of the God they worship.