John's theme of darkness and light describes two approaches to life. The way that is out of step with God is considered the way of darkness, while the way that is attuned to God is considered to be the way of light. But since we cannot necessarily see the difference with our eyes, how can we tell if someone is in fellowship with God? Are there signs we can look for to help us discern who is truly a friend? John suggests that one clue is to be found in an obedient lifestyle.