But Jesus said, "Do not forbid him, for no one who works a miracle in My name can soon afterward speak evil of Me.
for he who is not against us is on our side."
Mark 9:38-40 (NKJV)
To be exclusive means to limit or control something so that it is not easily accessible. For something to be inclusive, it would mean that the thing, some group for example, would include a larger number of people than a group that is exclusive. An exclusive group is not open or available to a large number of people, while an inclusive group is generally something that many people can be a part of. How exclusive or inclusive something is will usually be determined by the people who are already within that group or a part of that thing.
In Mark 9, two of Jesus' disciples found someone casting out demons in the Name of Jesus, and those disciples stopped him, because that person was not part of their group that followed Jesus. Those disciples were being exclusive and they believed that if someone was not following Jesus in the way that they were, then that person should be stopped. Did Jesus commend those disciples? No, Jesus told them to allow that person to continue with the good work they were doing, even if they were not in the same group with Jesus and His disciples.
There are many different church groups that have the core beliefs that Jesus is the Son of God and the Savior, and that the Bible is the Word of God. But there are other less relevant beliefs that these groups have, and this often leads to people becoming exclusive rather than inclusive, and doing things based on some church doctrine and not God's Word. While we should certainly not compromise our basic Bible beliefs, we should not be so exclusive and argue about minor points, but we should be as inclusive as possible and work with others to help people and preach the Gospel.