I have excerpted below from Lewis’ classic work Mere Christianity. The following paragraphs are for me, some of the most significant of the whole book. Admittedly, I stopped right when it gets good, but perhaps I will post that as well when my fingers are rested a bit
The better stuff a creature is made of- the cleverer and stronger and feer it is- then the better it will be if it goes right, but also the worse if it goes wrong. A cow cannot be very good or very bad; a dog can be both better and worse; a child better and worse still; an ordinary man, still more so; a man of genius, still more so; a superhuman spirit best- or worst- of all.
How did the Dark Power go wrong? Here, no doubt, we ask a question to which human beings cannot give an answer with any certainty. A reasonable (and traditional) guess, cased on our own experiences of going wrong, can, however, be offered. The moment you have a self at all, there is a possibility of putting yourself first- wanting to be the centre- wanting to be God, in fact. That was the sin of Satan: and that was the sin he taught to the human race. Some people think the fall of man had something to do with sex, but that is a mistake. (The story in the Book of Genesis rather suggests that some corruption in our sexual nature followed the fall and was its result, not its cause.) What Satan put into the heads of our remote ancestors was theidea that they could “be like gods”- cold set up on their own as if they had created themselves- be their own masters- invent some sort of happiness for themselves outside God, apart from God. And out of that hopeless attempt has come nearly all that we call human history- money, poverty, ambition, war, prostitution, empires, classes, slavery- the long terrible story of man trying to find something other than God which will make him happy.
The reason why it can never succeed is this. Godman us: invented us as a man invents an engine. A car is made to run on Gasoline, and it would not run on anything else. Now God designed the human machine to run on Himself. He Himself is the fuel our spirits were designed to burn, or the food our spirits were designed to feed on. There is no other. That is why it is just no good asking God to make us happy in our own way without bothering about religion. God cannot give us a happiness and peace apart from Himself, because it is not there. There is no such thing.
That is the key to history. Terrific energy is expended- civilisations are built up- excellent institutions devised; but each time something goes wrong. Some fatal flaw always brings the selfich adn cruel people to the top and it all slides back into misery and ruin. In fact, the machine conks. It seems to start up all right and runs a few yards, and then it breaks down. They are trying to run it on the wrong juice. That is what Satan has done to us humans.
C.S. Lewish, Mere Christianity (New York: Macmillan 1977) pg 54-55