Religion

I don't get these religions that say they are a "branch" of Christianity and believe in Jesus, or acknowledge Jesus as a true prophet, but then change/add to/take away/alter what Jesus taught. I just don't get it, I don't think I ever will. It makes no sense to me. If you believe that Jesus was who he said he was, and did what witnesses said he did, then how can you include him in your religion but yet change stuff?

If you believe in this Jesus, by default you have to you believe in the Christian Bible and the New Testament. At the end of the New Testament in Revelation (and in other places) it clearly warns about changing things written in the Bible:

"I warn everyone who hears the words of the prophecy of this book: If anyone adds anything to them, God will add to him the plagues described in this book. And if anyone takes words away from this book of prophecy, God will take away from him his share in the tree of life and in the holy city, which are described in this book."
Rev 22: 18-19

The only thing that does make sense to me is that the people of these religions have obviously been taught or shown a false Jesus. That's the only way they could "include" him in their religion, but not follow him, which is the greatest tragedy of all.