c. s. lewis

on marriage...

...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 [from marriage] 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...

...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...

(from "mere christianity" by c. s. lewis)