At this point I should like, in passing, to answer a question which has been put to me several times during these weeks: ‘Are you not aware that many are sitting in this class who are not Christians?’ I have always laughed and said: ‘That makes no difference to me.’ It would be quite dreadful if the faith of Christians should aim at sundering and separating one man from the others. It is in fact the strongest motive for collecting men and binding them together. And what binds is, quite simply and challengingly, at the same time the commission which the community has to deliver its message. If we consider the matter once more from the standpoint of the community, that is, from the standpoint of those who seriously wish to be Christians – ‘Lord, I believe: help Thou mine unbelief!’* - we must remember that everything will depend upon the Christians not painting for the non-Christians in word and deed a picture of the Lord or an idea of Christ, but on their succeeding with their human words and ideas in pointing to Christ Himself. For it is not the conception of Him, not the dogma of Christ that is the real Lord, but He is is attested to in the word of the Apostles. Be it said to those who account themselves believers: May it be given us not to set up an image, when we speak of Christ, a Christian idol, but in all out weakness point to Him who is the Lord and so, in the power of His Godhead, the sovereign decision upon the existence of every man. 

(Karl Barth, Dogmatics in Outline, pp. 93-94, ugly bold emphasis mine)

* Mark 9:24