I liked this exert from the Screwtape Letters because it takes a perspective that I have never thought of before. It is Sr. demon called Screwtape writing to his nephew. He instructs his nephew on how to corrupt a certain Christian. He tells his nephew to do it gradually, and slowly draw him away from God, because if he tried to do it to fast his patient would realize the trouble he was in and repent. Screwtape encourages his nephew to make the patient sin little by little. At the beginning he must just distract him from God, and eventually the patient will not even need a distraction to avoid Godly activity.
The perspective that Lewis takes makes us aware of the danger we all face. The devil will lure us away from God little by little so that we hardly even aware of the slippery slope that we are sliding down. The example of Lot and Abraham was a good example of how this can happen. Little by little Lot pitched his tent closer to Sodom, and closer to sin. Little by little his children fell into the worldliness and sin of Sodom until they refused to leave when the angels came and warned them of the impending destruction.
We must be cautious, because these subtle changes that the devil causes us to make can lead to the utter destruction of our soul. We must rely on the Lord, for without Him we cannot stand alone.