“Because I told you so.” I’m sure you remember hearing that as a child, and if you’re a parent, you’ve probably said that once in a while.

“Why should I do this?” “Because I told you so.” “Why should I not do that?” “Because I told you so.” That’s like the universal trump card parents have whenever their kids ask too many “why” questions. It’s probably saved countless parents from going insane when it seems like the “why” questions will never end.

But when it comes to sexual morality, I’m not sure that’s an adequate response.

Unfortunately, the only thing most Christians understand about the Bible’s view of sex is that you’re not supposed to do it unless you’re married. They have little clue why and little understanding of the way God designed sex to function.

Tim Keller makes some helpful observations about this. He explains the reason why God designed sex to function within the context of marriage. It’s because God knew that sexual relationships needed to be undergirded by the stability that comes from marital commitments.

Sex is an act that binds two people together on many different levels—emotional and spiritual as well as physical. And that’s why there’s supposed to be the safeguard of marriage commitment in place to make sure that bond isn’t painfully ripped apart.

Genesis 2:24 states God’s intention very clearly. It says, “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.” So according to this verse, God intends for a man and his wife to “become one flesh.” That means enjoy a complete personal union.

And that union doesn’t just rest on an emotional connection the way many people today assume. After all, it seems pretty unrealistic to think that mere emotion to serve as the basis for this union. Emotions come and emotions go. So God requires a covenant.

Covenants in the Bible are sacred agreements between two parties where they commit to doing certain things. And over and over again in the Bible we see covenant commitments serving as the foundation for significant relationships. God makes a covenant with Abraham, a covenant with Moses, a covenant with David, a covenant with the church.

God’s pattern is to protect significant relationships with covenant commitments. And following that pattern, he requires men and women to make a binding, public, and legal covenant with each other in the form of their wedding vows so that these covenant commitments can serve as the infrastructure for their intimacy.

The marriage covenant creates security in a relationship that makes it safe to be vulnerable. We’re only supposed to have that level of vulnerability and intimacy with someone who’s bindingly promised to be exclusively faithful to us rather than someone who’s under no obligation to stay with us even one more night.

I mean, think about it. We try not to make ourselves vulnerable in other areas of life. I’m friends with a lot of people, but I don’t give them my bank account information. I also don’t go dangerous neighborhoods at midnight to take a walk and get some fresh air. And would anyone buy a car if that car didn’t come with locks on the doors?

These are always we protect our vulnerabilities. And when you think about it, it just makes sense to do the same with our hearts and our emotions and the spiritual aspect of our being. It just makes sense to require a covenant.

That covenant is completed or consummated by the initial sex act. And then every time the married couple has sex after that, they’re renewing that covenant. It’s like they’re renewing their vows every time they have sex.

But when people engage in sexual immorality, it robs them of the safety and security of that covenant commitment. It robs them of enjoying intimacy in a healthy way.

And not only does sexual immorality rob people of healthy intimacy, but it also distorts the gospel. You see, God designed sex as a picture of the gospel.

When we were drowning in the filth of our sin and condemned before God with no way to help ourselves or rescue ourselves, God came to our rescue. He made a covenant commitment to love us and save us and make a way for us to be with him forever. And then he followed through with that by sending his son Jesus to this earth.

Jesus became a real human being and faced all the things we face but didn’t sin even one time. And then he died on the cross to take upon himself the punishment for our sins. All of the judgment and wrath that should have been directed toward us was directed toward Jesus instead. And then he resurrected from the dead and ascended into heaven as the victorious ruler of the universe.

And the Bible says he relates to the church—his people—the way a groom relates to his bride. In fact, the New Testament commonly speaks of the church as “the bride of Christ.”

Furthermore, there’s a unique and exclusive love that Jesus has for the church. Of course, he loves everyone in the world in a general way, but he loves his bride in a special way. It’s kind of like me, as a husband, having a special kind of love for my wife. It’s not that I don’t love other women, but there’s a uniqueness and an exclusivity to my love for Becky.

In the same way, there’s a sense in which God loves his bride exclusively. And it’s not like God just chooses every day whether he’s going to love his bride like that. No, he’s made a covenant commitment to his bride, to continue loving her that way, and we trust him to remain faithful to that commitment for all eternity.

So the gospel tells us a story of God loving his bride, redeeming his bride, and making a sacred commitment to remain faithful to his bride forever. But sexual immorality distorts that picture. It presents a different picture of God; it tells a different story about the gospel—a story where there’s no commitment and no need to be faithful. And in the end, it robs us of the glorious, pure, and beautiful picture of the gospel that God intended sex to be.