Of Waugh's later work, The Ordeal of Gilbert Pinfold is perhaps the least religious. It is an autobiographical account of hallucinations caused by drugs. Waugh was self-medicating for insomnia and coupled this with heavy drinking. However, we do have a Roman Catholic protagonist. While the protagonist does encounter some anti-Catholic prejudice, this is not one of the major themes of the book. Instead "the Box" itself is an almost prescient symbol of the intrusive power of modern technology.
The "Box" itself had an origin in Waugh's life at Stinchcombe, where he had a neighbor named Diana Oldridge who dabbled in spiritualism and similar fads and had a device called "the Box," which she believed to send out beneficial life waves that could cure diseases. At one point, Waugh believed that this object might be the source of his hallucinations. In the novel, Pinfold believes that the BBC correspondent Angel, the object of many of his paranoid fantasies, is using the Box to project voices into his cabin on the ship. When Pinfold finally returns to England and stops taking the drugs, he stops hearing voices.
Boxes have some specific Judaeo-Christian significance. The Ark of the Covenant is an important container or box in the Old Testament which contains the word of God. Orthodox Jews wear phylacteries, small boxes containing scrolls on which passages from the Torah are written. One should note that some of the fellow travelers on the boat think Pinfold is Jewish.
From a religious point of view, communication with God and the Devil can often be portrayed in terms of supernatural entities speaking through physical ones (a burning bush, a serpent, and so on). The Box thus acts as a modern source of the voice of God. However, Waugh tends to regard modernity with a certain suspicion and would likely view a box created by scientific technology as more likely to represent the work of the Devil.
The voices from the box can be read as an externalization of inner demons, good and bad. Margaret could be read as an emblem of woman as both Eve the temptress and the Virgin Mary who intercedes mercifully in human affairs. Pinfold's success over the voices can be read as a sort of faith journey in which the writer overcomes inner demons and writer's block to successfully produce the book we are reading.