The early church fathers understood it well for they knew there had to be a visible difference between a believer and an unbeliever. Here’s what Mathetes (130 AD) had to say:
For the Christians are distinguished from other men neither by country, nor language, nor the customs which they observe. For they neither inhabit cities of their own, nor employ a peculiar form of speech, nor lead a life which is marked out by any singularity. The course of conduct which they follow has not been devised by any speculation or deliberation of inquisitive men; nor do they, like some, proclaim themselves the advocates of any merely human doctrines. But, inhabiting Greek as well as barbarian cities, according as the lot of each of them has determined, and following the customs of the natives in respect to clothing, food, and the rest of their ordinary conduct, they display to us their wonderful and confessedly striking method of life. They dwell in their own countries, but simply as sojourners [or resident aliens].As resident aliens, these believers’ allegiance was elsewhere, their eyes set beyond the dictates of the times, their desires shaped not by the temporal.
As biblical as that may seem, I appreciate that being 'otherworldly-minded' tends to make killjoys of believers. At least that’s how it appears to a lot of people, not least the youth. At the end of our lesson, a college girl spoke up: “But we young people want to have fun.”
Are our lives so dour that we're curiously out of step with the abundant life promised by Jesus?