Many people try to understand Christians along a spectrum from “nominalism” at one end to “fanaticism” on the other. A nominal Christian is someone who is Christian in name only, who does not practice it and perhaps barely believes it. A fanatic is someone who is thought to over-believe and over-practice Christianity. In this schematic, the best kind of Christian would be someone in the middle, someone who doesn’t go all the way with it, who believes it but is not too devoted to it. The problem with this approach is that it assumes that the Christian faith is a basically a form of moral improvement. Intense Christians would therefore be intense moralists or, as they were called in Jesus’s time, Pharisees. Pharisaic people assume they are right with God because of their moral behavior and right doctrine. This leads naturally to feelings of superiority toward those who do not share their religiosity, and from there to various forms of abuse, exclusion, and oppression. This is the essence of what we think of as fanaticism.
What if, however, the essence of Christianity is salvation by grace, salvation not because of what we do but because of what Christ has done for us? Belief that you are accepted by God by sheer grace is profoundly humbling. The people who are fanatics, then, are so not because they are too committed to the gospel but because they’re not committed to it enough.Keller, Timothy (2008-02-14). The Reason for God (pp. 54-55). Penguin Group. Kindle Edition.