Sexual activity cannot run wherever it pleases. Our sexual desires have no right to satiated without limit. As we have seen, our sexual appetite and our sexual fulfillment are less important than protecting the weak, keeping our word, and loving our neighbor. The first step in having a rational, thoughtful conversation about the rightness and wrongness of certain kinds of sexual behavior is to recognize that virtually everyone believes there are rights and wrongs when it comes to sex.

Surely every Christian must acknowledge that the answer to the title of this post is “Yes, some sexual activity is wrong.” Every vice list in the New Testament includes “sexual immorality” or “impurity,” usually at the head of the list (see Mark 7:21-22; Rom. 1:24-31;13:13; 1 Cor. 6:9-10; Gal. 5:19-21; Col.3:5-9; 1 Tim. 1:9-10; Rev. 21:8). We can point out that God cares about other sins too or argue that Christians today make too much of sexual immorality, but no one can reasonably argue that the New Testament is indifferent toward sexual sin. Clearly, the Bible understands that certain sexual behaviors and lusts are illicit and that these behaviors and lusts can have no place in the life of a Christian.

Having established that point—one that should not be controversial if we are willing to take the New Testament on its own terms—the question then becomes, “What constitutes sexual immorality?” There is no honest way we can make the God of the Bible into the “God-of-anything-goes” when it comes to sex. As Christians, we must acknowledge that the Lord detests some sexual activity? And if “detest” sounds too strong to you, use “disapprove.” It will work just as well for this thought experiment.

So what kind of stuff should go in this category of “sexual immorality”? Without turning to any particular verses or doing any of the appropriate word studies, just think about the question logically for a moment. Virtually everyone agrees that some sexual behavior is wrong. Even the non-Christian, even the atheist, even the world’s worst/best libertine will tell you some sexual behavior is out of bounds.

Rape is wrong. No sane person would say otherwise. And why is rape wrong? Presumably, because one person is forcing another person to do what he or she doesn’t want to do. So, mutual consent is necessary for sex to be okay.

But is that all? What if a married man has sex with another man’s wife and both of them enjoy it and choose to keep having sex together? You have mutual consent. And yet, judging from the drama of reality TV and gossip headlines and the disgust over political scandals, most of us do not think adultery is okay. Sex can be wrong even when it pleases both parties and is freely chosen by everyone involved. Why? Because—I gather—we should not break our promises. Sexual activity is inappropriate if it means we hurt someone else by going against our word. Infidelity in any romantic relationship is wrong if monogamy was promised (like when married) or even implied (like when dating).

Are you keeping track? So far, we need mutual consent and faithfulness to our word for sex to be appropriate.

But what about sex with minors? Again, almost everyone is disgusted by adults having sexual encounters with children. Why? No promises are necessarily being broken. The perpetrators might even argue that there was some twisted form of mutual consent. And yet, we recognize the behavior is heinous because it takes advantage of children who are not in a position to defend themselves, assert their own opinions, or even discern all that is going on. Sex requires a certain maturity, the ability to understand our own bodies, and why and when and where we would allow others to be with us in an intimate way. This is, by the same reasoning, why most people consider it wrong for a man to have sex with a woman after she has been drinking too much. She’s not in a state to discern her situation or fully comprehend the consequences of what she is too ready to allow.

How about another scenario: Is it okay to have sex without telling someone you have a sexually transmitted disease? I imagine most people would conclude that such behavior is morally suspect. Why? Because one person’s pursuit of sexual gratification puts another person’s health at risk. It’s selfish and deceptive to engage in sexual activity which, unknown to the other party, adversely affects their well being.

And what about exaggerated sexuality at the Video Music Awards? Why was that so repugnant to so many people? Because people thought the performer was a different person? Because she has fans that want her to be sweet and innocent? Because some sexual behavior is distasteful and we’d rather not see it? It’s probably a combination of all of the above.

As you can see, sex is not the free for all people too easily make it out to be. Granted, I haven’t proven anything about sex before marriage, or sex with multiple partners, or sex with persons of the same gender, let alone anything about the definition of marriage. The purpose of this little thought experiment is more modest. I simply want to demonstrate that acceptable sex must involve more than self-expression or self-gratification. Even in our sex-crazed world almost all of us agree that sexual activity—if it is to be morally appropriate—must meet certain conditions.

• There must be mutual consent.
• We must not harm the well-being of others.
• We must not violate the principle of monogamy when it is promised or expected.
• Those engaged with us in a sexual encounter must possess a certain degree of discernment and self-awareness.
• Public standards of decency must not be transgressed.

Negatively, we can conclude that sex is not necessarily appropriate just because:

• It pleases us.
• It pleases everyone involved.
• It takes place between consenting adults.
• It is important to us.
• It is the embodiment of someone “coming of age.”

Sexual activity cannot run wherever it pleases. Our sexual desires have no right to satiated without limit. As we have seen, our sexual appetite and our sexual fulfillment are less important than protecting the weak, keeping our word, and loving our neighbor. The first step in having a rational, thoughtful conversation about the rightness and wrongness of certain kinds of sexual behavior is to recognize that virtually everyone believes there are rights and wrongs when it comes to sex.

We all believe in sexual immorality. The question is: what kind of stuff should go in that category? And on such a matter—so crucial for the health of our society, the stability of our families, and the safety of our souls—we would do well to examine all the resources at our disposal: the light of nature, common sense observations, and the witness of the Holy Spirit in the Word.

Kevin DeYoung has been the Senior Pastor at University Reformed Church (RCA) in East Lansing, Michigan since 2004. Kevin blogs at the Gospel Coalition; this article is reprinted with his permission.