“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 marriage) the grace which both partners ask, and receive, from God... "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.”