I wouldn't add that. This is what we were taught by the WT, but almost all Christians of many different denominations will tell you just the opposite.
The New Covenant that JESUS offered wasn't with a religion, it was with individuals who may find themselves in any number of the tens of thousands of Christian groups around the world.
In fact, exclusivity is one of the prime identifying characteristics of a cult.
Good point Sea Breeze. Your comment reminded me of the scripture at Matthew 18:20, where Jesus said the following about Christian fellowship.
"For where two or three gather in my name, there I am with them."
He didn't say anything about having to be an organized brotherhood to be his followers.