In Munster Bible College’s church history course today, we read from the second century Letter To Diognetus, which includes this description of Christians: 

“They live in their own native lands, but as sojourners; they share all things as citizens, and endure everything as foreigners. Every foreign land is a fatherland for them, and every fatherland a foreign land. They marry, like everyone else, have children, but they do not expose their infants. They share a common table, but not the marriage bed. They are in the flesh, but do not live according to the flesh. They spend [their days] on earth, but their citizenship is in heaven.”