How would a cat react if deprived of sleep? How does a car perform when deprived of oil? What happens to babies if no one holds them?
I don't know how the cat would react, but I bet it would grow highly irritable and eventually violent. The car, of course, would break down. And babies, I hear, lose all desire to eat if deprived of human affection.
This type of question–What would happen to X if starved of one of its most important elements–drove Walker Percy's fiction. But Percy applied the question to humans: What happens when people, either individually or as a culture, are deprived of religion? If we are spiritual beings, what happens when the spirit is suffocated?
Percy was a keen observer of the modern landscape and he saw into it deeply. He saw a modern existence that is devoid of meaning; lacking permanent things; without associations that instill meaning, like families are set up through the sacrament of marriage to instill stability and depth in the individual soul.