The Bible gives us numerous examples of people who refused to compromise to the ways of the world. We think of Joseph who fled from Potiphar's wife when she approached him with her sexual charms. We think of Daniel and his three friends who refused to drink the king's wine and eat his food. Again, Christians are to be in the world but not of the world. Christians are to be a light on a hill, the salt of the earth.
Christians are to be separate and different.
As we saw in the first lesson, the church has been called out by God and for God. Christ wants a church with walls. Jesus wants a fence put between us and the world. Yes, there are to be gates and doors in that wall - how else, then, could we witness to the lost and invite them in. But the point is, Jesus wants us to be different.