Excerpts from Christianity and Liberalism by J. Gresham Machen:
Is it true, then, that Christianity is not a doctrine but a life? The question can be settled only by an examination of the beginnings of Christianity. Recognition of that fact does not involve any acceptance of Christian belief; it is merely a matter of common sense and common honesty. At the foundation of the life of every corporation is the incorporation paper, in which the objects of the corporation are set forth. Other objects may be vastly more desirable than those objects, but if the directors use the name and the resources of the corporation to pursue the other objects they are acting ultra vires of the corporation. So it is with Christianity. It is perfectly conceivable that the originators of the Christian movement had no right to legislate for subsequent generations but at any rate they did have an inalienable right to legislate for all generations that should choose to bear the name of “Christian.” It is conceivable that Christianity may now have to be abandoned, and another religion substituted for it; but at any rate the question what Christianity is can be determined only by an examination of the beginnings of Christianity.. . .
. . . if any one fact is clear, on the basis of this evidence, it is that the Christian movement at its inception was not just a way of life in the modern sense, but a way of life founded upon a message. It was based, not upon mere feeling, not upon a mere program of work, but upon an account of facts. In other words it was based upon doctrine.
To answer the question succinctly – Christianity is a way of life that flows out of a specific doctrine.
What Christians believe has consequences for how they live. People can mimic the patterns of behavior, but that does not make them Christians. Only the doctrine creates Christians. That doctrine, if truly believed, flows into how one lives life.
EDITORIAL NOTE: Look for an upcoming series on AUTHENTIC CHRISTIANITY. The first installment will be released June 12.