Think of people you consider fanatical. They’re overbearing, self-righteous, opinionated, insensitive, and harsh. Why? It’s not because they are too Christian but because they are not Christian enough. They are fanatically zealous and courageous, but they are not fanatically humble, sensitive, loving, empathetic, forgiving, or understanding – as Christ was. Because they think of Christianity as a self-improvement program they emulate the Jesus of the whips in the temple, but not the Jesus who said, “Let him who is without sin cast the first stone” (John 8:7). What strikes us as overly fanatical is actually a failure to be fully committed to Christ and his gospel.
Timothy Keller. The Reason for God: Belief in an Age of Skepticism. Dutton Adult, 2008. 57.