In one of the more celebrated chapters of this book, Lewis takes on what he says is the most unpopular virtue: Chastity. Lewis's words here undermine the old show title "No Sex Please--We're British!" In his inimitable way, Lewis elucidates the Biblical standard and why it matters so profoundly for human flourishing.

In this chapter, Lewis explores the nature of psychoanalysis, rejects Freudian worldview assumptions, and reflects on the true nature of moral choice.

Lewis's discourse on Christian Behavior continues with this chapter on justice and society. His reflections and conclusions are fascinating and relevant: "...The real snag in all this drawing up of blueprints for a Christian society [is that] most of us are not really approaching the subject in order to find out what Christianity says: we are approaching it in the hope of finding support from Christianity for the views of our own party. We are looking for an ally where we are offered either a Master or a judge.

Lewis continues his discourse on Christian Behavior with this episode's chapter on the important topic of Virtue, focusing in on the "Cardinal" virtues of Prudence, Temperance, Justice, and Fortitude. It is a sad commentary on our times that those words seem so "old-fashioned" to our ears today.

This episode launches into Book 3 of Mere Christianity, which is entitled Christian Behavior. "The Three Parts of Morality" is a marvelous explication of moral theology, complete with some of Lewis's best analogies, and helps explain much of the confusion about morality that we see in our culture today.

Lewis describes what he calls "the Christ-life" within us and how we enter fully into that life. "The Christian... thinks any good he does comes from the Christ-life inside him. He does not think God will love us because we are good, but that God will make us good because He loves us; just as the roof of a greenhouse does not attract the sun because it is bright, but becomes bright because the sun shines on it."

Lewis weaves together the problem of man's need for redemption, the love of God expressed in the Incarnation, and the power of Christ's sacrifice on the Cross to change everything, reminding us that "...fallen man is not simply an imperfect creature who needs improvement: he is a rebel who must lay down his arms."

Lewis takes on the topics of God's goodness and free will, the search for happiness outside of God, the radical things that Jesus said about His identity, the forgiveness of sins, and concludes with his famous trilemma apologia.

As Lewis unpacks the ideas behind what Christians believe, this chapter, "The Invasion," looks at why atheism is too simple and why an "inoculation" idea of Christianity is inadequate, and points towards the good news that the rightful king has landed, albeit in enemy-occupied territory.

Following the great success of the first series of five broadcast talks, "Right and Wrong as a Clue to the Meaning of the Universe," the BBC asked Lewis to continue with a new series entitled "What Christians Believe." Lewis opens this series with his thoughts on "The Rival Conceptions of God," looking at ways that the religious impulse has animated mankind from ancient times.