False shepherds enter illegitimately and harm the flock.

John 10:1, 8, 10

¹Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, but climbeth up some other way, the same is a thief and a robber.

⁸All that ever came before me are thieves and robbers: but the sheep did not hear them.

¹⁰The thief cometh not, but for to steal, and to kill, and to destroy: I am come that they might have life, and that they might have it more abundantly.