I believe we must first ask what is suppose to be "strange" (unfamiliar) to us about this world before we can become "alien" to it.
Undoubtable all christians have come out of the "world" its only human! First John chapter 2 helps to explain what Christians are to keep away from, that which is naturaly part of unsaved human psyche.
Do Not Love the World
15Do not love the world or anything in the world. If anyone loves the world, the love of the Father is not in him. 16For everything in the world