Should Christians be separate from the world? Should we avoid associating with non believers? Certainly everyone can believe what they want and interpret the Bible in their own way.
Jesus says we are to love our enemies. Jesus ate with sinners and tax collecters. Followers of Jesus do not judge. Therefore it appears that Christians can associate with non believers and anyone they want to. They don't need to be separate from the world.
The problem of course is that because of their Christian's beliefs, some people won't associate with them.
We can look at what Jesus was saying in this way. Christians love everyone. They love the world and everyone in it just like God does. In fact when we love those who hate us we become sons of the Most High. Luke 6:35-37; We are all children of God no matter what we believe in. Since Christians don't judge they don't have a problem associating with non believers.
In other words, all we can control is ourselves. We can love everyone including our enemies. We can't control anybody else. We can try, but it doesn't work. If people in the world don't want to associate with us, we can't do anything about it.
Christians don't change their beliefs because some people hate what they say. In that way Christ brought divisions into the world. His beliefs were not popular with the Pharisees and leaders of his day and that's why he was hated by 'the world'. Likewise some people hate Christians today because their beliefs are different. It's not that Christians don't have friends with non believers, it's just that some non believers choose to reject Christians.
We can't do anything if we are hated for what we believe in. We can't control what others will do or say. We can only control what we will do and say. So while some people might want to separate themselves from us because they hate our beliefs, it doesn't mean that Christians separate themselves from the world. To do this would mean we are judging non believers and Jesus told us not to judge. Luke 6:27-41
Jesus didn't place any restrictions or rules upon his followers except that they love their neighbors and even enemies. Jesus himself set the example by eating with sinners and tax collectors.
The Apostle Paul added many rules and regulations to the words of Jesus. Paul was more judgmental. He was more concerned with righteousness and not associating with 'wicked' people. Why was that? Saul became the Apostle Paul. He converted to Christianity after Jesus died. Prior to then he was a avid persecutor of Christians. He was born and raised as a Pharisee. Get the Facts About The Apostle Paul to better understand why Paul placed more restrictions upon the early Christian congregation.