C.S. Lewis writes in his chapter on hope in Mere Christianity, "A continual looking forward to the eternal world is not ... a form of escapism or wishful thinking, but one of the things a Christian is meant to do. It does not mean that we are to leave the present world as it is. If you read history you will find that the Christians who did most for the present world were just those who thought most of the next. The Apostles themselves, who set on foot the conversion of the Roman Empire, the great men who built up the Middle Ages, the English Evangelicals who abolished the Slave Trade, all left their mark on Earth, precisely because their minds were occupied with Heaven. It is since Christians have largely ceased to think of the other world that they have become so ineffective in this. Aim at Heaven and you will get earth 'thrown in': aim at earth and you will get neither. It seems a strange rule, but something like it can be seen at work in other matters. Health is a great blessing, but the moment you make health one of your main, direct objects you start becoming a crank."
"Most of us find it very difficult to want 'Heaven' at all—except in so far as 'Heaven' means meeting again our friends who have died. One reason for this difficulty is that we have not been trained: our whole education tends to fix our minds on this world. Another reason is that when the real want for Heaven is present in us, we don't recognize it.... The longings that arise in us when we first fall in love, or first think of some foreign country, or first take up some subject that excites us, are longings that no marriage, no travel, no learning, can really satisfy.... There was something we grasped at, in that first moment of longing, which just fades away in the reality.... Now there are two wrong ways of dealing with that fact, and one right one.
- The Fool's Way—"He puts the blame on the things themselves. He goes ... thinking ... if only he tried another woman, or went for a more expensive holiday."
- The Way of the Disillusioned "Sensible Man"—"Of course," he says, "one feels like that when one's young. But by the time you get to my age you've given up chasing the rainbow's end." Supposing one really can reach the rainbow's end? It would be a pity to find out too late (a moment after death) that by our supposed "common sense" we had stifled in ourselves the faculty of enjoying it.
- The Christian Way—"The Christian says, 'Creatures are not born with desires unless satisfaction for those desires exists. A baby feels hunger: well, there is such a thing as food. A duckling wants to swim: well, there is such a thing as water. Men feel sexual desire: well, there is such a thing as sex. If I find in myself a desire that no experience in this world can satisfy, the most probable explanation is I was made for another world.... Probably earthly pleasures were never meant to satisfy it, but only to arouse it, to suggest the real thing.... I must ... never ... be unthankful for those earthly blessings, and ... never ... mistake them for the something else ... my true country, which I shall not find till after death.... I must make it the main object of life to press onto that other country and help others to do the same.'"
Highlights from chapter 10: Hope, book 3: Christian Behavior in Mere Christianity by C.S. Lewis. Click here for a clear view of how this chapter relates to the whole book.