Karth Barth, in a 1934 talk

For what we have experienced in Germany during these latter days — this remarkable apostasy of the Church to nationalism, and I am sure that every one of you is horrified and says in his heart: I thank thee, God, that I am not a German Christian! — I assure you that it will be the end of your road, too. It has its beginning with “Christian life” and ends in paganism. For, if you once admit, “Not only God but I also,” and if your heart is with the latter — and friends, that’s where you have it! — there is no stopping it. Let me assure you that there are many sincere and very lovely people among the German Christians. But it did not save them falling prey to this error.

Let me warn you now. If you make a start with “God and…” you are opening the doors to every demon….

In Germany we have learned by experience that the one thing that offered a chance to face the real enemy and refuse his claim was the simple message: God is the only Helper! It was the simple Either-Or which was refused a while ago. Learn in time what may here be learned. You are still soldiers in the barracks. Real firing has not yet begun for you. Some day you may be called to the front line. Perhaps there you will remember our discussion. You may then gain a better understanding of what you do not seem to be able to grasp today. One-sidedness will be your only chance.