This is my favorite assigned reading so far. He describes humans as having instinct but also along with that an overpowering Moral Law that everyone follows, or knows they should follow. This is not because of our upbringing, or the laws the government gives to us, it is a law that we did not invent, a law that is above us. An example Lewis uses is a piano: there are no right or wrong keys, every note is right at one time or wrong at one time to make the right tune.
Lewis comes up with so many fascinating insights, one of which I find particularly interesting. He says that an outside observer would have no knowledge of our "Moral Law". The observer would see only our actions, what we did do, and would not know that we have something telling us what we ought to do. And therefore since we are humans, we are the only ones aware of this above all moral code. In the same way, us, when observing nature, have no way to tell whether or not there is something behind or above the observed facts because we are studying from the outside. Lewis then uses this to point to a greater power, a creator. He says that we would not expect a creator to show up in creation because then we would not understand it. Instead, the being shows itself inside of us through the Moral Law that we only understand because it is within us. This is fascinating to me because it seems so logical. Lewis uses what humans can understand and then deductively proves it with in a logical way, making it understandable and believable.
This is why I enjoy Lewis. He does not bother, most of the time, with theological debate. He uses worldly, everyday knowledge to prove his point. I'm not saying that theology is bad, I am just saying that in the long run of things it does not prove anything except that people need faith. Most of the time this is not what people on the outside of belief need. I think Lewis understands this.