What Is "Mere Christianity" by C.S. Lewis About?

by Cynthia Tucker

"Mere Christianity" is a book by author C.S. Lewis, who is perhaps most famous for having written "The Chronicles of Narnia." The former book began as a series of recorded speeches given by Lewis to explain the basic teachings of Christianity. The book is divided into four "books": Right and Wrong, What Christians Believe, Christian Behavior and the Doctrine of the Trinity. Lewis' assessment of Christianity is even more interesting because he started out as an atheist, one who does not believe in God.

Right and Wrong

Lewis argues that everyone has an innate sense of right and wrong. Despite this knowledge of right and wrong, people often fail to practice the kind of behavior they expect from others. This innate sense of morality does not come from within humans, but from a law that no human created. There is something or someone beyond the universe guiding humans to do what is right and making them feel uncomfortable when they do wrong. The clue to who this "somebody" might be is found in two pieces of evidence: the design of the universe, and the moral law humans possess. This "somebody" is the being Christians know as God.

What Christians Believe

Christians believe in a God who loves good and hates evil. He has laws for behavior that He expects humans to abide by. The universe is at war because an angel, now known to us as the devil or Satan, rebelled. This rebellion disrupted the peace that God intended for the Earth. To counteract the consequences of the devil's rebellion, God came to earth in the form of a human named Jesus Christ. He came to die to pay for the sins of mankind, and to save sinners from eternal death. Christians have the promise of resurrection and eternal life because of Jesus' death and resurrection. One day Christ will return to destroy the devil and his power over this world.

Christian Behavior

Because God created humans for His own purposes, you don't have the authority to behave as if you belong only to yourself, but rather in such a way that you honor the Being who created you. God's rules for the treatment of others is summed up in the Golden Rule: "Treat others the way you want them to treat you." For example, God expects Christians to be sexually moral. This means you should not have sex unless you are married, and if you are married, you should have sex with no one other than your spouse. Christians should forgive others, practice humility, give to the poor, live by faith and look forward to their future lives, which they will spend in eternity with God.

The Doctrine of the Trinity

In old English, Christ is called the only "begotten" son of God. The active verb beget means to "become the father of." If you beget you create something of the same kind as yourself. Humans beget humans and animals beget animals. God can only beget God, someone of the same kind as Himself. Though Jesus appeared in human form, He existed with God from the beginning. There is only one God, but he exists as three beings: Father, Son and Holy Spirit. A Christian prays to God the Father through the prompting of God the Holy Spirit, who lives inside of him. Yet his full knowledge of God comes from God the Son, who came to earth to live a perfect life and die for the sins of many.


  • "Mere Christianity"; C.S. Lewis; 2001

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