Why Sex Belongs in Marriage

Sex is great and belongs in marriage. Yet, when it comes to sex, Catholics often get a bad rap. Many people look at our beliefs about sex, specifically our belief that it should be reserved for marriage, and conclude that we are simply puritans who think it’s dirty and needs to be limited as much as possible. However, this is about as far from the truth as you can get. We don’t believe that sex is bad or dirty; rather, we believe that sex should be reserved for marriage because it’s great. In fact, Catholics view sex as sacred, so we actually have a much higher opinion of it than the secular world does.

To many in our culture today, that may seem strange. The idea that Catholics think sex is dirty is so engrained in our culture that hearing what we actually believe about it can come as somewhat of a shock. In this article, I want to explore this shocking idea and look at sex from a Catholic perspective. I want to explain what makes it sacred and why that sacredness makes it perfectly suited to marriage and marriage alone.

“One Flesh” 

To begin, let’s take a look at what the Bible says about sex. Now, I am not interested here in the passages that say what kinds of sexual acts are and are not allowed. While those texts are important, they do not really get to the heart of the matter. They do not tell us what is so good about sex or why it is sacred, so I want to look at other passages. In particular, let’s start by looking at the very first book of the Bible.

When God created Adam, he realized that Adam was all alone in the paradise he had created for him (Genesis 2:18). To fix this, he made all the animals, hoping that one would prove to be a suitable companion, but none of them were (Genesis 2:19-20). Adam needed someone like him, another human being, so God created a woman, Eve, solving the problem. Adam immediately let out a great cry exclaiming how amazing she was (Genesis 2:21-23), and then the narrator interrupts the story and explains the significance of this event:

Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh. (Genesis 2:24)

This break in the narrative tells us that when a man and a woman get married, they become “one flesh,” although it doesn’t tell us what that means or what significance (if any) that fact has. Most people understand this to mean that spouses become one flesh when they consummate their marriage and have sex, but the text doesn’t say that explicitly. Nevertheless, we do not have to guess at its meaning. Fortunately for us, another book of the Bible explains it for us.

Not Just Marriage

Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never! Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, “The two will become one flesh.” (1 Corinthians 6:15-16)

In this passage, St. Paul does something interesting. He’s talking about having sex with prostitutes, and he quotes the “one flesh” passage from Genesis to help make his point. By doing so, he’s telling us that a man and a woman become one flesh any time they have sex, not just if they are married. Sex forms a real physical bond between two people, and Christians shouldn’t form that bond with prostitutes. Instead, as Genesis tells us, that union finds its proper place in marriage.

This is important because it forms the basis of the Church’s understanding of sex. Everything we Catholics believe about sex is based on this bond that it forms. That’s why it’s sacred, and that’s also why it should be reserved for marriage. However, this still leaves us with several questions: How exactly does sex unite people? Why is that union good? What does it have to do with marriage? To answer those questions, we need to take the Bible’s teaching about sex and marriage and reflect on it philosophically, exploring this “one flesh” union that sex creates.

The Wrong Answers

Let’s begin by looking at some things that sex is not. For example, it’s not just a fun activity that spouses enjoy doing together. If it were, then it would be no different from other fun activities like playing tennis or going to the movies, but it clearly is. Having sex with someone other than one’s spouse is blatant infidelity, but watching movies or playing tennis isn’t. Sex  is something spouses are allowed to do only with each other, so it shares in the exclusivity of the marriage itself. Consequently, sex is part of the very fabric of the marital relationship in a way that no mere fun activity ever could be.

Secondly, we can’t just say that sex brings a couple closer together emotionally because it is so intimate; that simply pushes the question back a step. What makes sex so intimate? Why is touching someone’s sexual organs different from, say, touching someone’s arm or their ears? Of course sex is intimate, but that doesn’t explain much. Rather, the intimacy of sex seems to be a consequence of the way it unites people. In other words, it is intimate precisely because it unites people so closely, not the other way around.

The Biological Answer

 So if sex is more than just a fun activity and if its intimacy is a consequence of the way it unites couples, then how exactly does it unite them as “one flesh”? I would suggest that, as the phrase “one flesh” implies, it unites them in a very physical, even biological, way. This may seem strange, but hear me out. Think of any biological process that our bodies perform, such as digestion, respiration, or movement. Whatever you think of, I can almost guarantee that it will have two features: 1) It’s performed by various organs working together for the good of the entire organism, and 2) It’s performed by only one person.

Let’s examine those two features, starting with the first one. What makes someone a single, unified organism rather than a collection of organs that just happen to be connected to one another is that those organs all work together for the good of the whole. For instance, in digestion, everything from our teeth to our intestines works together to break down our food and extract nutrients from it so the whole organism can benefit, and every other biological process is like that as well. They all involve various organs working together for the good of the whole.

The second feature, that these processes are all performed by a single person, may seem trivial. Of course we all digest our own food, move ourselves, and extract oxygen from the air on our own; this may seem like it should go without saying. However, I mention it because there is in fact an exception; there is one biological process that requires two people: reproduction. This one can only happen when a man and a woman join their reproductive organs in such a way that they work together for a single goal, the goal of producing a child who will carry on the genes of both parents.

The Reproductive Process

 And this, I would suggest, is what makes sex so special. When a man and a woman have sex, they unite biologically, becoming a single subject of a single biological act. In fact, we can even go so far as to say that they become like a single organism. Granted, they don’t literally become one person, but their organs work together for a single goal that benefits the whole (the couple), just like an individual person’s organs do in any other biological process, thereby creating a real biological union between them.

Now, this may not seem very romantic, but we have to keep in mind that we’re not just minds or souls trapped in bodies; no, our bodies really are us. We are composites of body and soul, and a soul without a body is just as incomplete as a body with only one arm or one leg. As a result, the biological unity that sex brings about is actually very personal. Since our bodies are us, sex unites two persons, not just two bodies, in a very intimate way, a way that nothing else ever could.

The Big Objection

Now, there is one objection that just about everybody rises to this view of sex: infertile couples. When infertile couples have sex, they can’t reproduce, so it seems like they don’t unite biologically. However, this objection misunderstands the nature of biological processes. To see what I mean, consider digestion. It begins when we chew our food, and it ends hours later after our stomachs and intestines have done their work. It’s a process that takes time, and that process can be interrupted, for instance by throwing up.

However, even if I throw up shortly after eating, I’ve still completed part of the digestive process. My organs have still been working together for a single goal, thereby functioning as a single, unified organism. Likewise, when an infertile couple has sex, they perform part of the reproductive process even though they cannot complete it. Nevertheless, by performing part of it, their reproductive organs still work together for the good of the whole, so they still join their bodies together and perform a biological process, thus becoming “one flesh.”

Sex and Marriage

 From all this, we can see why sex is sacred and why it belongs in marriage. It’s sacred because it unites two people in the most intimate way possible on the physical level. They give themselves to each other completely, and their bodies join together to become a single subject of a single biological act. They become, as it were, a single organism, and since we are organisms, that’s a very intimate union indeed. Once we understand this, it is easy to see why sex belongs within marriage. This is more than just an arbitrary rule; rather, it is based on the very nature of sex and marriage. Marriage is a complete union of two persons on every level (spiritual, emotional, physical, etc.), and sex is the physical part of that union. When spouses have sex, they embody (quite literally) the multi-level union that is their marriage.

As a result, sex fits marriage perfectly, but it’s misplaced in other contexts. For example, if a dating or engaged couple has sex, they are jumping the gun. Since they haven’t given themselves to each other completely in marriage, they are joining together in a way that is inappropriate for their current level of commitment. Moreover, if two people have sex just for pleasure, they are giving themselves to each other in the most intimate way possible and then using each other as objects for pleasure, whereas the proper response to such a gift of self is total love and acceptance. People deserve to be loved, so a complete gift of one’s self deserves to be met with nothing less. Consequently, the only context where sex fits is marriage. Only marriage can safeguard the sacredness of sex and the people who unite themselves to each other in it; only in marriage does a couple’s relationship fit the nature of act they’re performing.