Sexual Morality

Today's Scripture

Lewis now reaches the chapter he knew nobody wanted to hear. Before he says a word, notice that the Bible speaks about purity with hope, not disgust.

1 Thessalonians 4:3-4 — "For this is the will of God, your sanctification: that you abstain from sexual immorality; that each one of you know how to control his own body in holiness and honor."

Matthew 5:8 — "Blessed are the pure in heart, for they shall see God."

Psalm 51:10 — "Create in me a clean heart, O God, and renew a right spirit within me."

The Big Idea

Chastity is an old word for desire kept in its right place — faithfulness inside marriage, and waiting outside it. God is not against desire; he invented it and called it good. But our desires, like everything else in us, have been knocked out of order by sin. Today Lewis tells the truth about that — and then offers far more grace than anyone expects.

Reflection

The virtue nobody claps for

Lewis was giving these talks on BBC radio, to a whole nation listening in their kitchens and living rooms. When he reached this subject, he did not pretend it would go over well.

"Chastity is the most unpopular of the Christian virtues. There is no getting away from it; the old Christian rule is, 'Either marriage, with complete faithfulness to your partner, or else total abstinence.'" — C.S. Lewis, Mere Christianity

Two quick definitions, because these are old churchy words. Chastity means keeping sexual desire in its right place. Abstinence means waiting — saving sex for marriage. The Christian rule really is that simple, and really is that hard. It was unpopular in 1942. It is more unpopular now.

Paul taught the same rule to a young church in a city famous for doing whatever felt good. 1 Thessalonians 4:3-4 — "For this is the will of God, your sanctification: that you abstain from sexual immorality; that each one of you know how to control his own body in holiness and honor." Sanctification is another old word: it means God making you holy, little by little. Notice that Paul does not treat purity as a side issue for extra-serious Christians. He calls it the will of God for your life.

Lewis knew exactly how strange the rule sounds to modern ears, and he refused to soften it. Instead he drew the honest conclusion:

"This is so difficult and so contrary to our instincts, that obviously either Christianity is wrong or our sexual instinct, as it now is, has gone wrong. One or the other. Of course, being a Christian, I think it is the instinct which has gone wrong." — C.S. Lewis, Mere Christianity

Hold on to that little phrase: as it now is. Lewis is not saying desire is bad. He is saying something in us has slipped out of tune. And if we are honest, most of us already suspect he is right.

God is not embarrassed by bodies

Before going further, we have to clear away a lie that has hurt a lot of people: the idea that Christianity thinks bodies are shameful and sex is dirty. Lewis demolishes that in one sentence.

"Christianity is almost the only one of the great religions which thoroughly approves of the body — which believes that matter is good, that God Himself once took on a human body, that some kind of body is going to be given to us even in Heaven and is going to be an essential part of our happiness, our beauty and our energy." — C.S. Lewis, Mere Christianity

The very first page of the Bible backs him up. Genesis 1:31 — "And God saw everything that he had made, and behold, it was very good." That includes bodies. That includes marriage. God invented these gifts and pronounced them very good before sin ever touched the world. Christians did not come up with the idea that sex is shameful; we came up with the idea that it is sacred. Those are very different things.

So when God asks for purity, he is not sneering at something gross. He is guarding something precious. 1 Corinthians 6:19-20 — "Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, for you were bought with a price. So glorify God in your body." A temple is a place where God himself lives. Nobody posts a guard around a garbage can. You guard a temple because of what it holds.

An appetite gone out of order

But if desire is good, what exactly has gone wrong? Lewis answers with one of his most famous thought experiments. Imagine, he says, a country that has become obsessed with looking at food.

"Now suppose you came to a country where you could fill a theatre by simply bringing a covered plate on to the stage and then slowly lifting the cover so as to let every one see, just before the lights went out, that it contained a mutton chop or a bit of bacon, would you not think that in that country something had gone wrong with the appetite for food?" — C.S. Lewis, Mere Christianity

Of course you would. Hunger exists so that people eat and live. A packed theatre paying money to stare at a lamb chop is hunger unplugged from its purpose — an appetite spinning by itself, feeding on nothing. Lewis's point is that our culture treats sexual desire exactly the way that imaginary country treats food: stirred up constantly, sold for profit, and aimed at nothing real.

In Lewis's day it was posters and films. In ours, it follows us home in our pockets. Open almost any app and somebody is using this appetite to sell you something — clothes, music, games, shampoo. The advertisers are not wicked geniuses; they simply know which buttons are stuck in the on position. A desire that can be hooked that easily, that often, by that many strangers, is not a desire in healthy working order.

Here is the test Lewis is teaching us. A healthy appetite matches reality — it wants the right things, in the right amounts, for their real purpose. A perfect person's desires would fit the actual world the way hunger fits food. When a desire swells far past anything it was made for, the desire itself has gone wrong, no matter how natural it feels from the inside. Tim Keller gives the same diagnosis in different words:

"What is an idol? It is anything more important to you than God, anything that absorbs your heart and imagination more than God, anything you seek to give you what only God can give." — Tim Keller, Counterfeit Gods

That is what our world has done with sex: taken a good gift and asked it to be a god. And false gods always break the hearts that worship them.

The Bible's strategy is not to shame the desire but to re-aim the whole heart. Galatians 5:16 — "But I say, walk by the Spirit, and you will not gratify the desires of the flesh." Notice the order: walk by the Spirit first. Purity is not an empty heart; it is a heart filled with something better. That is why Matthew 5:8 is a promise, not a threat: "Blessed are the pure in heart, for they shall see God." The pure heart is not the one that wants nothing. It is the one whose wants point the right way — and what it receives, in the end, is God himself.

Grace for the ones who keep trying

Now comes the part of this chapter almost nobody sees coming. Having set the standard sky-high, Lewis turns around and speaks with startling gentleness to everyone who has already failed — which is everyone.

He would have understood Augustine, who admitted that as a young man, before his conversion, his honest prayer was:

"Give me chastity and continence, but not yet." — Augustine, Confessions

Be honest: that is how all of us pray about our favorite sins. Lord, change me — just not today. Augustine published that embarrassing prayer in a book, on purpose, because he wanted the world to know that God's grace had met him anyway.

King David shows us the first move after failure. After the worst moral collapse of his life, he did not hide or quit. He prayed Psalm 51:10 — "Create in me a clean heart, O God, and renew a right spirit within me." Create is the key word. David is not asking for a touch-up. He is asking God to do what only God can do — make something new out of nothing. Lewis says exactly the same:

"We may, indeed, be sure that perfect chastity — like perfect charity — will not be attained by any merely human efforts. You must ask for God's help. Even when you have done so, it may seem to you for a long time that no help, or less help than you need, is being given. Never mind. After each failure, ask forgiveness, pick yourself up, and try again." — C.S. Lewis, Mere Christianity

Ask forgiveness. Pick yourself up. Try again. That is not a counsel of despair; that is the actual rhythm of the Christian life. The prophet Micah turned it into a taunt against the enemy of our souls: Micah 7:8 — "Rejoice not over me, O my enemy; when I fall, I shall rise; when I sit in darkness, the LORD will be a light to me." Falling does not disqualify you. Staying down is the only way to lose.

None of this means making peace with sin. The old Puritan John Owen wrote one of the bluntest sentences in Christian history about that:

"Be killing sin or it will be killing you." — John Owen, The Mortification of Sin

The fight is real, and it matters. But Lewis noticed something surprising about what the fight is actually for:

"Very often what God first helps us towards is not the virtue itself but just this power of always trying again." — C.S. Lewis, Mere Christianity

Read that twice. God's first gift is often not instant victory but the strength to get back up. Why would he work that way? Because the long struggle teaches the soul its two most important lessons:

"We learn, on the one hand, that we cannot trust ourselves even in our best moments, and, on the other, that we need not despair even in our worst, for our failures are forgiven. The only fatal thing is to sit down content with anything less than perfection." — C.S. Lewis, Mere Christianity

We cannot trust ourselves. We need not despair. Both at once, held together. And both rest on a promise sturdier than our willpower: 1 John 1:9 — "If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness."

So today must end where Lewis ends — not with you gritting your teeth, but with Jesus. He is the one human being whose desires were perfectly matched to reality: pure in heart through every temptation we have ever faced. Hebrews 4:15-16 — "For we do not have a high priest who is unable to sympathize with our weaknesses, but one who in every respect has been tempted as we are, yet without sin. Let us then with confidence draw near to the throne of grace, that we may receive mercy and find grace to help in time of need." He fought the battle we keep losing, won it, and then died for the ones who lost. That is why Psalm 103:13-14 can say, "As a father shows compassion to his children, so the LORD shows compassion to those who fear him. For he knows our frame; he remembers that we are dust." God knows what you are made of. He is not standing over you waiting for the next failure. He is reaching down to help you up — again, and again, and again.

Going Deeper

Tonight, pray Psalm 51:10 slowly and in your own words — ask God to create, not just clean up. Then write Lewis's three-step rhythm somewhere you will see it this week: ask forgiveness, pick yourself up, try again. And if there is a struggle in this area you have been carrying alone, tell one trusted person — a parent, a pastor, a wise friend. Sin grows in the dark and shrinks in the light. You do not have to fight by willpower alone, and you were never meant to fight by yourself.