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. And the Christians believe that when He said this He was not expressing a sentiment but stating a fact-just as one is stating a fact when one says that a lock and its key are one mechanism, or that a violin and a bow are one musical instrument. 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.
As a consequence, Christianity teaches that marriage is for life. There is, of course, a difference here between different Churches: some do not admit divorce at all; some allow it reluctantly in very special cases. It is a great pity that Christians should disagree about such a question; but for, an ordinary layman the thing to notice is that the Churches all agree with one another about marriage a great deal more than any of them agrees with the outside world. I mean, they all regard divorce as something like cutting up a living body, as a kind of surgical operation. Some of them think the operation so violent that it cannot be done at all; others admit it as a desperate remedy in extreme cases. They are all agreed that it is more like having both your legs cut off than it is like dissolving a business partnership or even deserting a regiment. What they all disagree with is the modern view that it is a simple readjustment of partners, to be made whenever people feel they are no longer in love with one another, or when either of them falls in love with someone else.
Before we consider this modern view in its relation to chastity, we must not forget to consider it in relation to another virtue, namely justice. Justice, as I said before, includes the keeping of promises. Now everyone who has been married in a church has made a public, solemn promise to stick to his (or her) partner till death. The duty of keeping that promise has no special connection with sexual morality: it is in the same position as any other promise. If, as modern people are always telling us, the sexual impulse is just like all our other impulses, then it ought to be treated like all our other impulses; and as their indulgence is controlled by our promises, so should its be. If, as I think, it is not like all our other impulses, but is morbidly inflamed, then we should be specially careful not to let it lead us into dishonesty.
To this someone may reply that he regarded the promise made in church as a mere formality and never intended to keep it. Whom, then, was he trying to deceive when he made it? God? That was really very unwise. Himself? That was not very much wiser. The bride, or bridegroom, or the 'in-laws'? That was treacherous. Most often, I think, the couple (or one of them) hoped to deceive the public. They wanted the respectability that is attached to marriage without intending to pay the price: that is, they were impostors, they cheated. If they are still contented cheats, I have nothing to say to them: who would urge the high and hard duty of chastity on people who have not yet wished to be more honest? If they have now come to their senses and want to be honest, their promise, already made, constrains them. And this, you will see, comes under the heading of justice, not that of chastity. If people do not believe in permanent marriage, it is perhaps better that they should live together unmarried than that they should make vows they do not mean to keep. It is true that by living together without marriage they will be guilty (in Christian eyes) of fornication. But one fault is not mended by adding another: unchastity is not improved by adding perjury.
The idea that `being in love' is the only reason for remaining married really leaves no room for marriage as a contract or promise at all. If love is the whole thing, then the promise can add nothing; and if it adds nothing, then it should not be made. The curious thing is that lovers themselves, while they remain really in love, know this better than those who talk about love. As Chesterton pointed out, those who are in love have a natural inclination to bind themselves by promises. Love songs all over the world are full of vows of eternal constancy. The Christian law is not forcing upon the passion of love something which is foreign to that passion's own nature: it is demanding that lovers should take seriously something which their passion of itself impels them to do.
And, of course, the promise, made when I am in love and because I am in love, to be true to the beloved as long as I live, commits me to being true even if I cease to be in love. A promise must be about things that I can do, about actions: no one can promise to go on feeling in a certain way. He might as well promise never to have a headache or always to feel hungry. But what, it may be asked, is the use of keeping two people together if they are no longer in love? There are several sound, social reasons; to provide a home for their children, to protect the woman (who has probably sacrificed or damaged her own career by getting married) from being dropped whenever the man is tired of her. But there is also another reason of which I am very sure, though I find it a little hard to explain.
It is hard because so many people cannot be brought to realise that when B is better than C, A may be even better than B. They like thinking in terms of good and bad, not of good, better, and best ,or bad, worse and worst. They want to know whether you think patriotism a good thing: if you reply that it is, of course, far better than individual selfishness, but that it is inferior to universal charity and should always give way to universal charity when the two conflict, they think you are being evasive. They ask what you think of duelling. If you reply that it is far better to forgive a man than to fight a duel with him, but that even a duel might be better than a lifelong enmity which expresses itself in secret efforts to 'do the man down,' they go away complaining that you would not give them a straight answer. I hope no one will make this mistake about what I am now going to say.
What we call 'being in love' is a glorious state, and, in several ways, good for us. It helps to make us generous and courageous, it opens our eyes not only to the beauty of the beloved but to all beauty, and it subordinates (especially at first) our merely animal sexuality; in that sense, love is the great conqueror of lust. No one in his senses would deny that being in love is far better than either common sensuality or cold self-centredness. But, as I said before, 'the most dangerous thing you can do is to take any one impulse of our own nature and set it up as the thing you ought to follow at all costs'. Being in love is a good thing, but it is not the best thing. There are many things below it, but there are also things above it. You cannot make it the basis of a whole life. It is a noble feeling, but it is still a feeling. Now no feeling can be relied on to last in its full intensity, or even to last at all. Knowledge can last, principles can last, habits can last; but feelings come and go. And in fact, whatever people say, the state called 'being in love' usually does not last. If the old fairy-tale ending 'They lived happily ever after' is taken to mean 'They felt for the next fifty years exactly as they felt the day before they were married,' then it says what probably never was nor ever would be true, and would be highly undesirable if it were. Who could bear to live in that excitement for even five years? What would become of your work, your appetite, your sleep, your friendships? But, of course, ceasing to be 'in love' need not mean ceasing to love. Love in this second sense-love as distinct from 'being in love'-is not merely a feeling. It is a deep unity, maintained by the will and deliberately strengthened by habit; reinforced by (in Christian marriages) the grace which both partners ask, and receive, from God. They can have this love for each other even at those moments when they do not like each other; as you love yourself even when you do not like yourself. They can retain this love even when each would easily, if they allowed themselves, be 'in love' with someone else. 'Being in love' first moved them to promise fidelity: this quieter love enables them to keep the promise. It is on this love that the engine of marriage is run: being in love was the explosion that started it.