The Christians who did most for the present world were precisely 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 begun thinking less of the other world that they have become so ineffective in this. Aim at heaven and you get earth thrown in; aim at earth and you get neither.

- CS Lewis, Mere Christianity