To sum up all in one word— what the soul is in the body, that are Christians 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, yet is not of the body; and Christians dwell in the world, yet are not of the world. The invisible soul is guarded by the visible body, and Christians are known indeed to be in the world, but their godliness remains invisible. The flesh hates the soul, and wars against it, though itself suffering no injury, because it is prevented from enjoying pleasures; the world also hates the Christians, though in nowise injured, because they abjure pleasures. The soul loves the flesh that hates it, and [loves also] the members; Christians likewise love those that hate them. The soul is imprisoned in the body, yet preserves that very body; and Christians are confined in the world as in a prison, and yet they are the preservers of the world.
-Unknown, Epistle of Diognetus, Chapter XIX, Ante-Nicene Fathers Volume I, Kindle Location 1741