Barth, CD I/2, p. 430-431:

The fellow-man who is unaware of his true plight, the fellow-man to whom we can look and about whom we can concern ourselves, above all the fellow-man who helps us confirm and enhance us in the role of benefactor, mentor and ameliorator: this fellow-man does not constitute any serious problem, and any headaches which he may incidentally cause will not be mortal. But this in the last resort not at all disconcerting fellow-man is not our neighbour in the sense of the second commandment.  He is not the one who, sent and authorised by God, shows mercy upon us. He is lacking in the most important quality, in which alone he could do so, an actual similarity to the crucified Jesus Christ. At least, he is so in our eyes and in his relation to us. That is why he is not at all disconcerting.  That is why we do not experience any serious unwillingness in relation to him.  But that is also why he cannot help us seriously. This fellow-man will not summon us to the praise of God. Only afflicted, sinful fellow-man can do that.  Only this man is my neighbour in the sense of the second commandment.  But this neighbour will cause me a really mortal headache.  I mean, he will seriously give me cause involuntarily to repudiate his existence and in that way to put myself in serious danger. In face of this neighbour I certainly have to admit to myself that I would really prefer to exist in some other way than in this co-existence. I would prefer this because from this neighbour a shadow falls inexorably and devastatingly upon myself. The wretched fellow-man beside me simply reveals to me in his existence my own misery. For can I see him in the futility and impotence of his attempt to live, without at once mutatis mutandis recognising myself? If I really see him, if as propinquissimus he is brought into such close contact with me that, unconfused by any intersecting feelings which may influence me, I can only see his misery, how can it be otherwise? This is the criterion: if it is otherwise, if I can still see him without seeing myself, then for all the direct sympathy I may have for him, for all the zeal and sacrifice I may perhaps offer him, I have not really seen him. He remains at root that in no way disconcerting fellow-man. He is still not my neighbour. The neighbour shows me that I myself am a sinner.

This passage, which really needs its greater context to fully explain itself, is so characteristic of Barth's style, at least to the extent I've read him so far.

It's a strange new world...

This bit of Barth, it seems to me, has something to say to the question of why short-term missions are taking off, while local dying neighborhoods continue to experience neglect.