Below is a portion of another one of Barth’s Letters. A bit strongly worded, but perhaps this is exactly what must be said to those who say many true things, but do not “speak the truth in love” (Eph. 4:15)?
You say many correct things. But what is correct is not always true. Only what is said kindly is true. You do not speak kindly in a single line.You utter a powerful No on all possible sides. It is indeed necessary to say No too. But the right No can only be one which derives from and is upheld by an even more powerful Yes. I hear you say only No.
You accuse. That, too, has to be done. But again, if this is Christian accusation, it has to be enclosed in the promise, in the glad tidings of God’s grace. In you it is naked accusation.
You demand that others repent. Sometimes one must dare to do this. But only he may do so who himself repents and lives in repentance. You preach down from your high horse, righteous amid the unrighteous, pure among the impure.
Dear Mr. N.N., I am in my eighty-third year; I am ahead of you by many years along with their experience of life, and I can only say: It cannot be done as you are trying to do it in your book. A Christian should not speak as you do either to his fellow-Christians or to his fellow-man, nor should the church speak thus to the world.
Geoffrey Bromily (trans.), Karl Barth Letters: 1961-1968, #316 (p. 328-329)
It seems to be an open question as to whether Barth himself always practiced this. His famous and emphatic No to his friend Emil Brunner’s natural theology may have been written without a corresponding Yes (and it certainly damaged their friendship)…. though he does spell out his own position on this subject in more detail in his Church Dogmatics (basically, his No to natural theology corresponds to his Yes to the revelation of God in Jesus Christ, CD I.1/I.2). Late in life he seems to have regretted his harsh tone to Brunner, sending out very personal messages to him via his family (when Brunner was on his deathbed), to make sure that his final Yes to Brunner (the person) was heard. Maybe a little late ?