Most humans are very protective of their tribe, their closest group of friends and family. The cohesiveness that took years to form is usually not open to new members. We are very cautious about adding people to our tight-knit group because loosening it might make it vulnerable. On top of that, the group might change or get divided.
The trust factor makes it even more likely that a new person will not be accepted into the group. They usually remain outside the circle if they have been known to be mean-spirited, argumentative, and dangerous. Why would the group ever put their sweet fellowship in danger?
That is how the first group of disciples viewed Paul: a danger to the group. "And when he had come to Jerusalem, he attempted to join the disciples. And they were all afraid of him, for they did not believe that he was a disciple." - Acts 9:26, ESV. The disciples of Jesus were human, too. He was only received on the testimony of Barnabas, who had grown to know Paul.
Here's the applicable truth: We need to be protective of our groupings, especially of the church, the bride of Christ. What God has formed is special. Hence, there is a need for Next Steps at the church and relationship building over time before allowing new people into your family and friends groups. There are wolves out there.
However, Jesus is in the business of saving and changing people. He adds people to His church who were previously adamantly opposed to its welfare. God introduces His people to each other for companionship and fellowship. Those who God has truly added cannot be ignored or discarded for no reason.
So, be cautious and protective of your groups, but be open to the fact that God changes people. - Pastor Mike
BTW, what should you do if you're attacked by a group of clowns? Go straight for the juggler.