I have been rereading Helmut Thelicke – “Life Can Begin Again. Sermons On The Sermon On The Mount”. He was a Pastor in Germany and preached during the worst of the War even to holding services in the bombed out shell of his Church in Stuttgart. Whatever we might think of his theology he was a great preacher. Here he is on salt –
Most Christians are stupid. That is to say, disobedience is always stupidity (in the full sense in which the godless are called fools), though most people think that it is wisdom and prudence that prompts them to disobedience. I noted, for example, during the church struggle with Hitler, when hard and often dangerous decisions had to be made, that when a person could not summon up the courage to be obedient and blindly trust God's promises he always had the shrewdest arguments and most elaborate tactical reasons for making his disobedient, and in the long run stupid, compromises. So it is in this case, the Christian remains in the saltcellar because he thinks that here he will be best preserved. He wants to be wise, he wants to be sharp— and in the very act loses his saltness. Salt works, salt remains salt only as it gives of itself.