Christianity is not a religion. For whatever is human about it, all the manifestations in which it may resemble a religion, are merely the echo or reflection of a movement that does not proceed from man or have to be carried out by him, but happens to him and has to be responded to by him, a movement by a being of an entirely different kind. Alone among all the religions, Christianity is essentially a pointer, pointing backwards and forwards and in either case upwards ... a movement that differs from all religions, all human leaps and superstructures, and is indeed opposed to all religion.
If Christianity is properly understood, that is, on the basis of the historical sources, the documentation of its origins in the Old and New Testaments -- and that, incidentally, is the task of theology -- it is impossible to shut one's eyes to the realization that, in contrast to religion, its essence is not man's arising to go to God, but God's arising to go to man....
"Christian", properly understood, means being governed by the message of Jesus Christ, the liberating discovery of God's gracious move towards humanity. But such discovery is an event, not a condition or institution, and thus is not an attribute with which human creations can be endowed or by which they can be distinguished.
Karl Barth (1963)