Fierce wolves will come in among you, not sparing the flock

"Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves ...." (Matthew 7:15)   

 because  "I know that after my departure," said Paul, "fierce wolves will come in among you, not sparing the flock; and from among your own selves will arise men speaking twisted things, to draw away the disciples after them" (Acts 20:29-30).  

He also said: "stand fast in one spirit, with one mind striving together for the faith of the gospel " (Philippians 1:27);