Q. 71. What is required in the seventh commandment?

A. The seventh commandment requireth the preservation of our own and our neighbor’s chastity, in heart, speech, and behavior.

When you sleep with your Catharine and embrace her, you should think: “This child of man, this wonderful creature of God has been given to me by my Christ. May He be praised and glorified.” On the evening of the day on which, according to my calculations, you will receive this, I shall make love to my Catharine as you make love to yours, and thus we will be united in love.

Of course we’re living together. Don’t worry, pastor, we are planning on getting married.” “Yes, I know the Bible’s rules about sex outside of marriage, but what’s the big deal? It’s not like I’m hurting anyone, and besides, I can’t get married for a while, and I have these needs.” “Sure, God teaches we aren’t supposed to do that—usually. But my situation is different.” “Where does it say that engaged couples can’t have sex? Show me the verse.” “I can’t understand why you told my kid that she’s sinning. What are you trying to do—drive her away from the church?”

Evangelical pastors and youth workers are increasingly hearing these kinds of things when they try to instruct and admonish professing believers on biblical chastity.1 As a Christian college professor teaching marriage and family courses, I often hear remonstrations like these from my students. More and more evangelicals acknowledge what the Bible teaches in these areas yet dismiss it generally or individually. Others use convoluted reasoning to explain away the “rules.” Parents trying to hold the line on these issues find themselves increasingly fighting an uphill battle against not only the outside world but against their children’s evangelical peers and even other adults in their churches. Why is it that so many who claim to believe the Scriptures and love the Lord no longer find biblical teaching on sex to be compelling?

Evangelicals who talk like this often view themselves as sophisticated and well-informed on sexual matters compared to narrow and out-of-date traditionalists who are hopelessly hung up and behind the times. However, comments like these actually reveal that those who make them do not understand or appreciate the biblical teachings about sexuality nearly as well as they think they do. Their vision for sex is cramped and inferior next to what God truly teaches us about this wonderful gift he has given to humankind.

God’s perfect plan and foundation for human society combines qualities that our limited minds often consider opposites. His plan is uncomplicated but complex; plain but lovely; earthy but spiritual; regulating but liberating; guileless but mysterious; simple but difficult; humble but lofty; limiting but liberating; common but sacred. It is the enjoyment of sexual intimacy and—God willing—the procreation and rearing of children. It is doing so only within the exclusive, lifelong, covenantal union of a man and a woman united as one flesh through the divinely ordained institution of holy matrimony. It is marriage united to sex and children.

That God’s moral law binds sex to lifelong, exclusive marital bonds between one man and one woman has never been contested by any wing of orthodox Christianity. This clear ethic cuts through all the sexual what-ifs that have been tossed out to try to obfuscate the obvious and rationalize our way out of submission to God’s commands. In recent history, we have seen accelerating waves of assaults on many long-established, timeless Christian truths. These are coming not only from atheists or those claiming to be members of rival faiths but from professing Christians. Typically, they claim to be taking “fresh looks” at key portions of Scripture whose plain meaning conflicts with modern Western culture. While theological liberalism has long questioned the accounts of miraculous events in Scripture, this has more recently expanded to refuting basic moral claims. Nowhere is this more evident than in Christian doctrines related to sexuality and sexual identity.

There have always been those who claim to be Christians but reject Christian sexual mores, but they have typically been those who have given up any serious commitment to uphold any biblical teaching that clashes with modern sensibilities, prejudices, or practices. In recent times, though, there are many who profess the lordship of Jesus Christ and submission to biblical revelation who are abandoning the teaching that sexual intimacy is only legitimate and truly good between a man and a woman who are married to each other. This ranges from carving out exceptions to wholesale abandonment.

The sexual practices of professing Christians increasingly reflect their growing compromise or relinquishment of the biblical sexual ethic. Sex outside marriage—up to and including cohabitation and multiple partners over time—is now widely practiced by many who regard themselves as conservative Protestants. Among Protestants, those who embrace and seek to live by the plain teachings of the Bible on sex are increasingly rare.

When I was a new believer, freshly converted from the hippie lifestyle during the Jesus Movement in the mid-1970s, a nice woman moved in with the man next door. She was a Bible-believing, even fundamentalist, Christian. She posted lots of Scripture verses and other religious messages in the kitchen. It appears they eventually married. Still, as a young believer, I found their sexual cohabitation shocking. How could she reconcile this behavior with the clear teachings of the Bible? This kind of thing no longer surprises me.

Where do we begin if we want to turn the professing church back toward fidelity to the biblical sexual ethic? It will take more than mere sermonizing. But we do need to start with solid teaching on sexual relationships, with instruction that avoids both the modern error of carnal license and the more ancient mistake of being hostile to even marital erotic love. Both misguided teachings harm people and dishonor God.

Teaching about sex should not be primarily learning and enforcing rules derived from biblical proof texts. Yes, there are commandments about sex and they ought to be taken seriously, but those requirements exist within a larger order created and maintained by God and ultimately point to truth about him and the reality that he called into existence. They are ultimately about achieving our highest purpose as human beings, which is to glorify and enjoy God.2

In this chapter, I will introduce the understanding of marriage—and, with it, sex and the human body—that flows out of creation itself. In particular, I want to show how this helps us see what it means for two to become one flesh and how this represents both the Trinity and the relationship between Christ and the church. I will also consider how the creation account established a unique and powerful understanding of the physical body, which has profound implications for sex. After laying this foundation, I will explore teaching in the Bible about sexual immorality in general, and sex outside marriage in particular, looking first at the Old and then the New Testaments. Following this, I will consider “celibacy” and “chastity” as they have been presented in the Bible and understood by the Protestant Reformers. Finally, I will point to the hope and redemption that all of us who have failed to obey God sexually are offered freely in our Savior, the Lord Jesus Christ.

Now, let us start where God starts—in the book of Genesis.

The heart of this teaching is embedded in Genesis 1:27–28 and 2:7–8, 18–24. Here we learn that humankind was created as male and female, in the image of God: “So God created man in his own image, in the image of God he created him; male and female he created them” (1:27). We see in these passages that marriage is a procreative union (“Be fruitful and multiply and fill the earth,” 1:28) of man and woman as one flesh (“Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh,” 2:24). We also learn here that the marital relationship is not just about sex or procreation, but it is designed to provide men and women with mutual help and companionship (2:18) as they serve and obey the Lord (1:26, 28; 2:15–17) and enjoy his abundant provisions together (1:29; 2:9, 16).

A man shall leave his mother, and a woman leave her home. They shall travel on to where the two shall be as one. As it was in the beginning, is now until the end, woman draws her life from man and gives it back again. And there is love.4

In addition to the public ceremony and covenantal vows we associate with the wedding ceremony, we have always understood that the one-flesh relationship is uniquely revealed, physically, in vaginal sexual intercourse. This reality is in many respects a mystery that is hard to adequately describe. A pastor friend said to me once, “The one-flesh union has a transcendent quality that is expressed physically.”5 In an extensive discourse on Genesis 2:24, René Gehring notes that the connection between sex and the one-flesh marital bond is widely accepted among biblical scholars.6 Sherif Girgis and his coauthors point out that the nature of marriage as a “comprehensive union” requires that the husband and wife experience this “bodily union.”7

It is significant that in the Old Testament the Hebrew word yada is not only used for sex (Genesis 4:1, 17, 25; 19:5; Num 31:17) but for many variations of the basic concept “to know.”8 As Greg Smalley has written, “Sex as knowing … implies discovery, actively pursuing knowledge about your spouse.” It means seeing into and revealing oneself to another at a deep level of emotional intimacy and vulnerability. Smalley writes, “God’s idea of yada is for you to know your spouse completely, for you to be deeply known by your spouse and for both of you to enjoy each other sexually.”9 This was meant by God to be for husband and wife alone. No one but my spouse has the right to know me in this way, nor do I have the right to know anyone but my spouse in this way.

In fact, sexual intercourse is viewed as the consummation of a marriage.10 Provisions in the Mosaic law demonstrate that the new husband and wife were expected to engage in this marital act following their public vows (Deut 22:13–21). The Puritans (as most people did in their day) did not believe a marriage existed until the couple had sexual intercourse following the public vows.11

When Martin Luther married former nun Katharina von Bora, he took this quite seriously. In fact, their sexual consummation was literally witnessed by his good friend Justus Jonas, following local custom.12 I do not recommend this; I doubt there are any today who face the unique challenges of an ex-priest and an ex-nun proving they had truly married against the background of vehement opposition from the medieval Catholic Church. Still, Luther’s decision shows just how centrally he viewed sex in sealing true marriage.

Certainly, the one-flesh reality of marriage cannot be reduced to the sexual relationship alone. It encompasses the totality of the marital bond. It cuts across every dimension of the relationship of husband and wife. However, the sealing of the marital bond in sexual intercourse is vital and powerful in not only its symbolism but in its reality. For example, Paul forbids married people from unnecessarily abstaining from sexual intercourse for lengthy periods of time (1 Corinthians 7:5).

The very nature and place of sexual intercourse in the one-flesh union of marriage makes clear that it is exclusively for the marital bond and not to be engaged in outside of that relationship. In virtually all orthodox expressions of Protestantism, sexual fulfillment is seen as one of marriage’s fundamental purposes. In the Anglican matrimonial service’s declarations of the purposes of marriage, it states, “It was ordained for a remedy against sin, and to avoid fornication; that such persons as have not the gift of continence might marry, and keep themselves undefiled members of Christ’s body.”13 Paul states categorically that marriage is the only place in which sexual expression is permitted (1 Corinthians 7:9), as does the writer of Hebrews (13:4).

Lest we miss the point regarding the inherent one-flesh nature of sexual intercourse, Paul makes it clear, citing Genesis 2:24: “Or do you not know that he who is joined to a prostitute becomes one body with her? For, as it is written, ‘The two will become one flesh’ ” (1 Corinthians 6:16). As John Calvin suggests regarding this passage, sex outside of marriage corrupts something that God has designed for marriage, and doing so brings a curse rather than a blessing.14

Sex is delightful, beautiful, and wholesome in its proper place. It is a good gift of God, as is our desire for sex. But out of its place it becomes perverted, a mockery of this lovely blessing and the God who gifted it to the human race. To truly appreciate a fine painting, we place it in a frame and setting that is appropriate to it and enables its inherent qualities and message to be experienced fully. If we take the same painting, put it i...