The Devil's Advocate

"In the Catholic Church, for anything to pass as a TRUE miracle, it must be open to a third-party investigation. The third-party must be an independent person who plays the devil's advocate.

I'm still trying to understand why we have different sect in a religion yet we claim to serve the same God?? One sect see themselves as Deputy Jesus, meanwhile looking at the other sect like Devil's Advocate ?‍♀️?‍♀️?‍♀️.