Jesus corrected the disciples when they wanted to stop someone who was not one of them from using the name of Christ. Our immediate response is to think that he is telling us all that we should be careful not to exclude people who want to join themselves to Christ and use his power for good. We know that Jesus was a friend of outcasts and sinners. Unless they are clearly enemies it appears we should treat them as if they one with us. We all have some experience of the difference between an inclusive attitude and an exclusive loyalty to a group.
Marriage is a good example of an exclusive kind of loyalty.
On the other hand when it comes to welcoming children into a family, we readily accept an new addition. Being a follower of Jesus can give people a strong sense of their own identity. People from all sorts of different backgrounds, different colours and nationalities, etc., can make up a great diversity in the church. That is a theme commonly proclaimed and believed, almost as if it were the gospel the itself. But the gospel is not the same thing as saying that all sorts of different people can be included in a Christian fellowship.