Book III: Chapter 8 The Great Sin Summary and Analysis

Lewis believes that the greatest sin in Christianity is pride. He sees other serious sins emerging from pride: greed, conceit and power lust. The other sins involve some level of goodness about them. Drinking to excess could also involve laughter, illicit sex might involve a level of love, but pride has nothing good about it. It is at its essence competitive, with one person wanting to be better than others, or richer, or more powerful, and this becomes an all-consuming desire that leads away from God and directly into the devil's arms.

Lewis sees apparently pious people eaten up by pride. He predicts they will not attain Heaven, as Jesus has never known these people. They may have preached in His name, but that does not matter.

On the other hand...