Cheever introduces the reader to a typical, ordinary couple, the Westcotts, gives us background information about their lives. They appear to have a well balanced, happy life. Then the new radio comes into the story, by way of Jim. And the Westcott's reality is turned upside down.
There is an element of the supernatural introduced into the plot with the radio. The Westcotts now exist in two worlds, the real world and the murky world created by the radio.
As a symbol, the radio is a corrupter of morals, luring one into an addiction to listening to the intimate secrets of others. Its like being a peeping Tom, looking in the windows of other while they dress and undress.
It suggests voyerism, or watching the actions of others, like through binoculars, while not interacting with them, is a problem that can happen to anyone.
One theme that is expressed in this story is the lure of addiction. And, how, the most ordinary looking people, can be hiding a secret life.
Things are not always what they appear, the author tries to tell us, the most innocent, upstanding, proper individuals, can be serial killers, drug users, or domestic abusers, or voyeurs.