To sum it up . . . . What the soul is in the body, that Christians are in the world. The soul is dispersed through all the members of the body, and christians are scattered through all the cities of the world. The soul dwells in the body, and yet is not the body, and Christians dwell in the world, but are not "of the world." The invisible soul is guarded by the visible body; in the same way, Christians are indeed to be in the world, but their godliness remains invisible. Epistle to Diognetus (appx. 130 CE)
One of the earliest examples of Christian apologetics
Written to pagan world
Abstract: "We are OK; we aren't here to overthrow the order, just bless it"
The Christians cannot be distinguished from other people by country, or language or custom they observe. For they neither inhabit cities of their own, nor employ a peculiar from of speech, nor lead a life which is marked out by any singularity. The course of conduct which they follow has not devised by any speculation or deliberation of inquisitive minds [SB: philosophy]; nor do they, like some, proclaim themselves the advocates of any merely human doctrines. But, inhabiting Greek as well as barbarian cities, according to the lot each of them has been cast, and following the customs of their nationality in respect to clothing, food, and the rest of their ordinary conduct, [yet] they display to us their wonderful and confessedly striking method of life.ibid.