Book Review – The Purity Principle

(The following post is from a friend and avid reader who wishes to remain anonymous. We asked him to write up some book reviews for our blog. This is his first installment.)

The Purity Principle is a concise 100 page book that contains Randy Alcorn’s impassioned plea for readers to live a life of sexual purity. Unlike some books on sexuality, Randy Alcorn writes for a broad audience and avoids vividly describing sexual impurity. The fundamental premise that underlies the book’s message is what Alcorn describes as “The Purity Principle: purity is always smart; impurity is always stupid” (16). Whenever we choose sin, we suffer. “A holy God made the universe in such a way that actions true to His character, and the laws derived from his character, are always rewarded. Actions that violate His character, however, are always punished” (16, emphasis original). Alcorn continues, “it’s okay to be out there ‘for yourself’ on this issue” (22). The rest of Alcorn’s book is the explication of this principle with practical steps for guarding sexual purity.

A Thoroughly Practical Book

One of the strongest facets of The Purity Principle is its exigent call to action and its thorough practicality. To be sure, the book’s practicality does not lie in the ease of carrying out Alcorn’s vision of a sexually pure life. Instead, the practicality of Alcorn’s words lies in Alcorn’s ability to provide tangible and embodied examples of what the pure life may well require. For example, Alcorn devotes an entire chapter to Getting Radical (chapter 7). Alcorn tells the story of a man who struggled with watching salacious television programs until he began telling the hotel attendants to remove the television from his room upon check-in (55).

Similarly, Alcorn tells us to confront our own excuses about falling into sexual sin by rhetorically asking, “If someone put a gun to your head and said he would pull the trigger if you looked at pornography, would you do it?” (59). Later, Alcorn excoriates those who complain about making sacrifices in the battle for sexual purity by saying, “Followers of Jesus have endured torture and given their lives in obedience to him. And we’re whining about giving up cable . . . Purity only comes to those who truly want it” (68-69).

Some will undoubtedly consider Alcorn’s advice legalism and separationalism. For example, Alcorn writes, “if you can’t be around women wearing swimsuits without looking and lusting, then don’t go on vacation where women wear swimsuits . . . If it means being unable to go on a church-sponsored retreat, don’t go” (66). Alcorn seems to adopt the attitude, albeit implicitly, that changing behavior is the crucial issue. Although he states that thoughts must change, little time is devoted to how the heart changes—except a comparison to expunging arsenic that is intended to urge individuals to avoid viewing pornography in order to purify their heart. How does this mesh with Jesus’ teaching in Matthew 15:19 that “out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false testimony, slander”? Still, for all its focus on externals, we must respect Alcorn’s ardor and realize that sexual sin not something to play with.

An Appeal to Self-Interest

A second strength of The Purity Principle is its appeal to self-interest. As Christians from Augustine to Edwards and Lewis to Piper have written, humans want to be happy. It is unalterably imprinted within our nature to seek happiness. The question is not whether we will seek happiness but where we will seek it. It is with this mindset that Alcorn quotes from John Piper’s book Future Grace to lay forth the positive implication of this theological truth: “We must fight [lust] with a massive promise of superior happiness. We must swallow up the little flicker of lust’s pleasure in the conflagration of holy satisfaction” (39).

An implication of this teaching (developing a mindset to resist temptation) is laid out early by Alcorn: “Satan’s greatest victories and our biggest defeats come when he gets us to ask, ‘Should I choose what God commands’ . . . ‘or should I do what’s best for me.’ The very framing of the question shows how deceived we are?” (18). Alcorn also makes a negative application of his belief about self-interest in pleading with readers to pursue sexual purity. This time, Alcorn implores the members of his to avoid sin because it’s not in their interest: “Those who’ve succumbed to sexual temptation did not do so in their self-interest” (23). The power of Alcorn’s words to tie the battle for sexual purity in with humanity’s unalterable desire to be happy—a desire that is intended to lead to God, but often leads to sin as it did in Eden—is a formidable strength. Many books on purity ring empty and fall short because they subtly and insidiously require a pernicious asceticism that sabotages the very thing it seeks to strengthen.

A potential weakness of this approach is that some might derive a simplistic conception of sin as always being punished and good as always being rewarded. While the Bible teaches that this is true from an eternal perspective, this belief does not seem to match up with the yearnings of the brokenhearted Psalmist or the experiences of the proud sinner. How does one reconcile Alcorn’s message with David’s lament that those who did evil seemed to succeed. Similarly, how does one make sense of the ecstatic students describing wild parties overflowing with pursuits of sexual sin? What about rational and respectable adults who avidly contend that their live-in relationship promotes stability, love, and happiness? To be sure, Alcorn would respond that those who sin do so because “they pursued what they imagined was their self-interest” (23). To some, Alcorn’s words may ring shallow and simplistic on this point—even if his point is true in the final analysis.


For all its strengths, The Purity Principle contains some shortcomings. First, this book is not for those recently crushed by grievous sexual impurity. This is not the book to hand to the pastor who just confessed an extramarital affair to his church two days after a congregant discovered the adultery. The potential for this book to engender despair and foster hopelessness is real.

Second, Alcorn’s book is not theologically rich. While the reader will learn a plethora of helpful tips and be admonished by a litany of warnings, there is virtually nothing distinctively Christian about the book. With a quotation from a different series of Holy Books, The Purity Principle could just as easily be a call to sexual integrity from a Jewish or Islamic scholar. Some would argue that this is permissible: it’s the behavior modification, not the cause of that modification, which matters. Perhaps this has merit. Nonetheless, as one theologian said, the test to evaluate whether a book or sermon is truly Christian is not whether it quotes Scripture, but whether Jesus had to die in order for the message to be true.

A Book of Wise Strategies

Alcorn’s work is concise, applicable, and accessible, making The Purity Principle appealing to readers of all stripes. Alcorn avoids complicated theology or diction and instead focuses on tips to walking in sexual integrity amidst a society in love with impurity. In addition to a chapter entitled “Wise Strategies,” Alcorn discusses setting boundaries, acquiring Internet filters, avoiding lust triggers, entering accountability, and much more. Although these topics are hardly unique to Alcorn’s work, a concise accessibility accents Alcorn’s words.