A reference at a site I visit inspired me to pull down Dorothy L. Sayers' collection of essays, Creed or Chaos (1949), and turn to the title essay (c. 1940), an essay that has continuing relevance. Sayers:
.... There is a great difference between believing a thing to be right and not doing it, on the one hand, and, on the other, energetically practising evil in the firm conviction that it is good. In theological language, the one is mortal sin, which is bad enough; the other is the sin against the Holy Ghost, which is without forgiveness simply and solely because the sinner has not the remotest idea that he is sinning at all. So long as we are aware that we are wicked, we are not corrupt beyond all hope. Our present dissatisfaction with ourselves is a good sign. We have only to be careful that we do not get too disheartened and abashed to do anything about it all. ....
The thing I am here to say to you is this: that it is worse than useless for Christians to talk about the importance of Christian morality, unless they are prepared to take their stand upon the fundamentals of Christian theology. It is a lie to say that dogma does not matter; it matters enormously. It is fatal to let people suppose that Christianity is only a mode of feeling; it is vitally necessary to insist that it is first and foremost a rational explanation of the universe. It is hopeless to offer Christianity as a vaguely idealistic aspiration of a simple and consoling kind; it is, on the contrary, a hard, tough, exacting, and complex doctrine, steeped in a drastic and uncompromising realism. And it is fatal to imagine that everybody knows quite well what Christianity is and needs only a little encouragement to practise it. The brutal fact is that in this Christian country not one person in a hundred has the faintest notion what the Church teaches about God or man or society or the person of Jesus Christ. If you think I am exaggerating, ask the Army chaplains. ....
It is not true at all that dogma is "hopelessly irrelevant" to the life and thought of the average man. What is true is that ministers of the Christian religion often assert that it is, present it for consideration as though it were, and, in fact, by their faulty exposition of it make it so. The central dogma of the Incarnation is that by which relevance stands or falls. If Christ was only man, then He is entirely irrelevant to any thought about God; if He is only God, then He is entirely irrelevant to any experience of human life. It is, in the strictest sense, necessary to the salvation of relevance that a man should believe rightly the Incarnation of Our Lord Jesus Christ. Unless he believes rightly, there is not the faintest reason why he should believe at all. And in that case, it is wholly irrelevant to chatter about "Christian principles." ....
Dorothy L. Sayers, "Creed or Chaos" in Creed or Chaos, Harcourt, Brace & Co., 1949, pp. 25-45.