Why are there so many division within the a religion?

Because people interpret things differently and want to believe it (what they believe) their way.

For example: Even when Paul the Apostle was still alive and preaching the Word, he had to deal with this very problem.

Some said they were followers of Jesus, some said Paul, etc. He tried to explain there should be no confusion about this, he was not crucified for their sins. That the church should not become divided like this. Today, some people believe in the gifts of the Holy Spirit others do not, and it goes on and on.

I am sure this is what happen in many religions.