Above the entrance to the philosophy department at the University of Southern California, where Dallas Willard has taught for forty years, is a figure of Diogenes. The fourth century B.C. philosopher was known to carry a lamp through the streets of Athens in the daylight in search of one honest man. To some Diogenes was a madman; to others he was a provocative revealer of truth.

Willard's ideas elicit similar reactions today. His books on spiritual formation have served as beacons to Christians seeking a fuller understanding of the kingdom of God. To those who believe the church's message requires no adjustment, Willard seems foolish, carrying a light where none is needed.

Willard appeals to those haunted by the question: Why don't Christians look more like Christ? To those bothered by the statistics indicating in the areas of divorce, materialism, sexual promiscuity, racism, and physical abuse, that American Christians behave no differently than the culture around them.

The problem, Willard ...