What Ideas Does C.S. Lewis Cover in Mere Christianity?

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Mere Christianity is a work of Christian apologetics about the core beliefs of Christianity that transcend the different denominations within the faith. In the book’s foreword, Lewis emphasizes not offering any one expression of Christianity as the objectively correct one. Instead, Lewis focuses on the faith’s central beliefs as stated in the Apostles Creed and The Book of Common Prayer. The Apostles Creed was written in the early church in the third century to affirm the core beliefs of Christianity to guard against different heresies. The Book of Common Prayer was compiled by the Archbishop of Canterbury, Thomas Cranmer, in 1549. It is an Anglican liturgical book based on Scripture and the Apostles Creed

Lewis’ argument begins by contrasting subjective morality with objective morality. He uses examples of good and evil not being mere preferences for different cultures but an objective reality that human beings on an everyday basis with the freedom to choose either. For historical evidence of this, Lewis compiled a list of common moralities all over the world in The Abolition of Man, which he references in Mere Christianity.

Lewis argues that this objective moral law points to a law maker. He then describes the differences between dualism, pantheism, and theism and challenges the view that Jesus of Nazareth was simply a good moral teacher. In Lewis’ view, Jesus is the same Jesus of faith and history and gives his Lord, Liar, or Lunatic trilemma argument. How does one simply view Jesus of Nazareth as a good moral teacher if he claims to be God? If He is not God, He is either a raving lunatic or a devil. Lewis got the idea for this argument from G.K. Chesterton’s The Everlasting Man. 

In the remainder of Mere Christianity, Lewis discusses prayer, the trinity, sexual morality, the theological virtues of faith, hope, and love, and what happens to someone when they surrender their lives to Christ. By coming to a place of surrender and repenting, an individual’s heart and mind are transformed by the agape love of Christ, and they become a new creation, as St. Paul states in 2 Corinthians 3.

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