"Being in love is a good thing, but it is not the best thing. There are many things below it, but there are many things above it. You cannot make it the basis of a whole life. It is a noble feeling, but it is still a feeling… knowledge can last, principles can last, habits can last; but feelings come and go… 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 times when they do not like each other; as you love yourself even when you do not like yourself. “Being in love” first moved them to promise fidelity: this quieter love enables them to keep the promise. It is on this level that the engine of marriage is run: being in love was the explosion that started it."