White Horse Inn interviewed Os Guinness recently; I adapted part of it for our Sunday School discussion on how we should interact with culture, how we often get it wrong, and how understanding common grace is the key.
Here's a quick explanation:
Be IW not OW: how we should be
Be IW, OW: Christians that look just like the world
Not IW, Not OW: Christians that have withdrawn from society
Not IW, OW: Pharisees, the prodigal son's older brother, a Christian ghetto
A proper understanding of common grace is the key to staying in the "IW not OW" quadrant. Forget about common grace and you tend to separate from the world. Forget that common grace is not saving grace and you end up OW.