These quotes are from Mere Christianity, by C.S. Lewis. Book III chapter 10 Hope.
"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 inffective in this. Aim at Heaven and you will get earth "thrown in": aim at earth and you will get neither."
"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."
"I must keep alive in myself the desire for my true country, which I shall not find till after death; I must never let it get snowed under or turned aside; I must make it the main object of life to press on to that other country and to help others to do the same."
Food for thought . . . Thoughts for Prayer