What metaphors are used in Mere Christianity by C. S. Lewis?

Morality is made up of three parts, according to Lewis. The first part is the relationships between human and human, the part of morality that most people think about. The second is the inner human, an individual's care of self. Lewis likens this to an oceangoing ship and how well the engines run, the steering gears work, and everything which makes the craft seaworthy. The third part of morality consists of the relationship between a human and the power that made the human.

Lewis believes that the problem with morality is that most people only think about the first part, their relationships with each other. A common rationalization is if a person does no harm to another person, the behavior in question must be moral. Lewis uses two analogies to point out the problem with this narrow thinking, a convoy of ships and a band playing music. If the only thing to be concerned about in the convoy is not running into each other, then the internal mechanics of each ship might be ignored, and the ultimate destination might turn out to be wrong. The convoy might end up in Calcutta instead of the desired destination, New York. As for the band, each musician might not get in the way of the others, but the overall musical piece could be wrong for the occasion. The two metaphors sometimes mix during this explanation.