[Ideology] comes about as [one] thinks he can and should ascribe to the presuppositions and sketches he has achieved by his remarkable ability, not just a provisional and transitory but a permanent normativity, not just one that is relative but one that is absolute, not just one that is human but one that is quasi-divine. His hypotheses become for him theses behind which he no longer ventures to go back with seeking, questioning, and researching. He thinks that they can be thought and formulated definitively as thoughts that are not merely useful but instrinsically true and therefore binding. His ideal becomes an idol. He thinks that he knows only unshakable principles and among them a basic principle in relation to which he must coordinate and develop them as a whole, combining them all, and with them his perceptions and concepts, into a system, making of his ideas an ideology. Here again the reins slip out of his hands. This creature of his, the ideology, seems to be so wonderfully glorious and exerts on him such a fascination that he thinks he should move and think and act more and more within its framework and under its direction, since salvation can be achieved only through the works of its law. This ideology becomes the object of his reflection, the backbone and norm of his disposition, the guiding star of his action. All his calculations, exertions, and efforts are now predestined by it. They roll towards its further confirmation and triumph like balls on a steep slope. Man’s whole loyalty is loyalty to the line demanded by it. He thinks that he possesses it, but in truth it already possesses him. In relation to it he is no longer the free man who thought he had found it in its glory and should help to put it on the throne. He now ventures to ask and answer only within its schema. He must now orient himself to it. He must represent it as its more or less authentic witness and go to work as its great or small priest and prophet. At root he no longer has anything of his own to say. He can only mouth the piece dictated to him as intelligibly as he can, and perhaps like a mere parrot. His own face threatens already to disappear behind the mask that he must wear as its representative. He already measures and evaluates others only from the standpoint of whether they are supporters of this ideology, or whether they might become such, or whether they might at least be useful to it even without their consent, or whether they must be fought as its enemies. Its glory has already become for him the solution not only to the personal problem of his own life but to each and all of the problems of the world.
~ Karl Barth, The Christian Life: Church Dogmatics IV/4, Lecture Fragments, 225.