The  effects of Mark 16:9-21 not belonging to The Bible

1. It removes our authority over Satan and his works and implies all the miracles of healing and the casting out of demons could not be from Jesus as we did not have his delegated authority to do so.  So it was either from our own authority (A lie) or from Satan (a bigger lie).  Either way Satan is glorified so the removal of this passage cannot be correct.

2. It stops us demonstrating The Kingdom of God and the authority it has over Satan so we have no real proof it exists except from the words of Jesus.

3. It makes evangelism just another set of words that compete with the words of other religions because there is no miraculous to make it stand out from them. It is the miraculous in evangelism that shows Christianity is special.

4. It removes the special relationship we have with God that shows we belong to His Kingdom.

It is obvious why Satan desired this passage to be removed from The Bible