If you read history you will find that the Christians begin the most for the present world are just the ones that thought the most of the next. The Apostles themselves, who set on foot. in 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 one 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 in effective in this. And that Heaven and you'll get the earth "thrown in": aim at earth and you'll get neither.
C.S. Lewis, C.S. Lewis's Mere Christianity
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