Screwtape XVIII-XXI

1. Ch. XVIII. "To be" means "to be in competition"(Lewis 94).  This quote is saying that life is a battle of the fittest.  Everything that exists in the world fights for their existance.  It's basically every man for himself.  If a being stops fighting, he would be wiped out by another being. 
2. Ch. XIX. "He must have some real motive for creating them and taking so much trouble about them." (Lewis 100).  In this quote, Screwtape is saying that the "Enemy" (God) created man yet it is a mystery why He created man and still takes care of man although they have fallen.  However, as Christians, the reason why God created man was for His own glory.  Although man has fallen into sin, God still cares and loves us so much that He sent his only son to die for us.  However, the devil and his followers try to cloud the minds of man so that they would not be able to understand God and see how much He loves them. 
3. Ch. XX.  "The aim is to guide each sex away from those members of the other with whom spiritually helpful, happy, and fertile marriages are most likely."  (Lewis 106).  This quote is saying that the goal of the devil is to try to draw humans away from a good Christian relationship.  To do this, the devil uses earthly things such as fashion and art to try distract a person's mind from good.  They would start to focus on their appearance and spend less time focusing on the relationship that God says we should have. 
4. Ch. XXI.  "A period of sexual temptation is an excellent time for working in a subordinate attack on the patient's peevishness." (Lewis 111).   This quote speaks of a time when the devil could attack a person.  During this time, the person has a very low toleration for anything.  When the person is angered, he/she would do anything to relieve their stress and anger.  Therefore, the devil uses sexual temptations during this time to turn man away from God.