Screwtape deconstructs the history of marriage:
Now comes the joke. The Enemy described a married couple as ‘one flesh’. He did not say ‘a happily married couple’ or ‘a couple who married because they were in love’, but you can make the humans ignore that. You can also make them forget that the man they call Paul did not confine it to married couples. Mere copulation, for him, makes ‘one flesh’. You can thus get the humans to accept as rhetorical eulogies of ‘being in love’ what were in fact plain descriptions of the real significance of sexual intercourse. The truth is that wherever a man lies with a woman, there, whether they like it or not, a transcendental relation is set up between them which must be eternally enjoyed or eternally endured. From the true statement that this transcendental relation was intended to produce, and, if obediently entered into, too often will produce, affection and the family, humans can be made to infer the false belief that the blend of affection, fear, and desire which they call ‘being in love’ is the only thing that makes marriage either happy or holy. The error is easy to produce because ‘being in love’ does very often, in Western Europe, precede marriages which are made in obedience to the Enemy’s designs, that is, with the intention of fidelity, fertility and good will; just as religious emotion very often, but not always, attends conversion.
—from The Screwtape Letters