While the novel is fantastic, it deals with a serious subject. Lewis calls it "the inner ring". Organizations typically have groups of people who are more powerful or influential than others. These rings admit some people and exclude others. There may be rings inside rings.
The desire to be inside, to gain acceptance and approval, can be a powerful motivation for some people. This desire can be used by those on the inside to manipulate those seeking admission. This is a major theme of the novel, as a main character struggles between his desire to be inside and his qualms about the nature of the conspiracy in which he has become enmeshed.
Lewis elaborated on these themes in a classic essay entitled The Inner Ring. The best line in the essay is the following:
Of all the passions, the passion for the Inner Ring is most skillful in making a man who is not yet a very bad man do very bad things.While the danger of the inner ring may occur in many settings, it is particularly relevant in politics. Most people get involved in politics because they want to do good. But once there, some fall to the allure of power. They seek power first and abandon principle. Most of them, though, are simply being manipulated by those higher up.
Those starting out in politics would do well to take Lewis' advice. Abandon the desire to be inside. Then you will no longer be a slave to the desires of others, but can do good with a clear conscience.