4 You adulterous people, don’t you know that friendship with the world is hatred toward God?
James gives us yet another mark of the Christ-follower: he says that Christ-followers separate themselves from the world, it's ways and its thinking.
So does that mean that we must live in monasteries and not have anything to do with those who are not Christ-followers? The answer is a resounding no! What we are called to do is to live in the world but not fall prey to its ways and thinking. We are to be insulated from the world but not isolated from it. That requires careful attention daily to what we listen to, who we spend most of our time with (willingly), etc. It is an issue of carefully guarding yourself and then washing yourself daily with the Word so as not to fall prey to the world's ways. It requires that we spend time with other Christ-followers who can help to point out the blind spots where we may be slipping into a world's way of thinking.
Be on your guard, it is easy to get sucked into the ways of the world but if we put up proper boundaries we can be Christ-followers who live in this world but are not of this world.