This essay by Rowan Williams (HT Jason) fits nicely into the diaspora theme of this blog, and also relates to my recent altercation with Steve Douglas ;-), here's an excert.
. . . one of the mainsprings of Christian self-understanding in the formative years of the Church's life was the idea that the believer was essentially a 'migrant', someone who was in any and every situation poised between being at home and being a stranger. In the New Testament and a good deal of the literature that survives from the first couple of Christian centuries, one of the commonest self-descriptions of the Church is in the language that would have been used in the Mediterranean cities for a community of migrant workers, temporary residents.
As a 'resident alien' in whatever society he or she inhabited, the believer would be involved in discovering what in that society could be endorsed and celebrated and what should be challenged. The Christian, you could say, was present precisely as someone who was under an obligation to extend or enrich the argument - sometimes indeed to initiate the argument about lasting social goods in settings where there was previously no possibility of thinking about what made a social order good or just or legitimate.
In the context of a religiously diverse modern society, something of this role is bound to be played by all communities of faith, to the extent that they operate with different ideas of accountability from those that mostly prevail around them; they believe they are accountable to transcendent truths or states of affairs. But it is worth noting how deeply and distinctively this language is embedded in early Christian literature. And this suggests that, if it is the case that the stranger is always necessary to make any society think about itself both critically and hopefully, the believer's role is always, in modern societies, going to show some intriguing parallels with that of the refugee intellectual.