Sex without permanence, like a gospel without permanence, provides no safety at all, only a miserable striving after what cannot be grasped. Without the joy and security of marital permanence, it utterly fails in its purpose to point to the joy and security of the gospel.
A recent discussion in my home centered around a television episode in which the “happy ending” consisted of the hero and heroine deciding to move in together but not get married. I suspect most readers of this post do not believe that that is truly a happy ending. But why? Is it just because God says so? Well, that would be enough, but there is more to say about it—God has given us more.
First, we must understand that sex, in its true form, is inseparable from marriage. This is more than just saying that marriage is the only proper context for sexual expression. It means that the very essence of sex, as its Creator designed it, includes it being an expression of the marital union. You can see this if you do a study of the passages in Scripture that use the phrase “the two shall become one flesh.” This phrase refers most literally to sex itself, but it also refers to the whole marriage union, of which sex is the physical expression. C.S. Lewis explained it this way:
The Christian idea of marriage is based on Christ’s words that a man and wife are to be regarded as a single organism—for that is what the words “one flesh” would be in modern English.… The inventor of the human machine was telling us that its two halves, the male and the female, were made to be combined together in pairs, not simply on the sexual level, but totally combined. The monstrosity of sexual intercourse outside marriage is that those who indulge in it are trying to isolate one kind of union (the sexual) from all the other kinds of union which were intended to go along with it and make up the total union. The Christian attitude does not mean that there is anything wrong about sexual pleasure, any more than about the pleasure of eating. It means that you must not isolate that pleasure and try to get it by itself, any more than you ought to try to get the pleasures of taste without swallowing and digesting, by chewing things and spitting them out again.¹
Sex as a physical union has its meaning only in the context of the relational, emotional, legal union that is the whole marriage. So while Paul speaks of sex with a prostitute as “becoming one flesh” (1 Corinthians 6:16), he does so only to point out how horribly such sex fails in its God-intended meaning. That meaning is only properly expressed when sex is an expression of the marriage union. Just like a word out of context can actually carry a different meaning, so, too, sexual activity outside of the context of marriage carries a meaning different than that for which God designed it.
And that God-intended meaning is nothing less than the gospel itself. In both 1 Corinthians 6:12–20 and Ephesians 5:25–32, the union termed as “the two shall become one flesh” is described as pointing to our union with Christ. And because sex is inseparable from marriage, it is not just marriage as a one-flesh union, but also sex as the physical expression of that union that is meant to picture the union of Christ and his Bride, the Church. Sex as an expression of marital union speaks the gospel; sex independent of marriage speaks anti-gospel.