How can you tell if a prophet is true or false? Jesus has a very simple solution: “By their fruits you can recognize them” (Matthew 7:15-20). False prophets deceive in appearance but inwardly are ferocious wolves. Fruit, Jesus says, is what enables us to discern them. And fruit has to do with behaviors.
Thornbushes don’t produce grapes; thistles don’t produce figs. Bad people don’t produce good works — so Jesus is saying. Good trees produce good fruit; bad trees produce bad fruit. So says Jesus. There is a correlation between heart and behavior.

Jesus is speaking here about folks who claim to be his followers, who are known for prophetic gifts and behaviors, but are frauds. And the way to know the fraud from the follower is by fruit. Plain and simple (and not that this solves everything), how one behaves tells alot.
Jesus’ point is that we are to recognize when leaders are not genuine and when they are “ferocious wolves” — that is, leaders who are intent on devouring others, using others, consuming others for their own advantage, for their own benefit — the picture seems clear to me. And Jesus is dealing here with clear stereotypes. Just wait, he says, the ravenous will soon be eating and devouring other folk.
It may take time; and we may find ourselves committed to them and listening to them and learning them but, eventually so it seems, character will win out and we will see them for who they are by the way they behave. As Dale Allison says, “False face cannot hide false heart forever.”
The text encourages two things: first, it exhorts to inspect ourselves and, second, it exhorts to watch and discern the ravenous from the shepherd who feeds his or her flock with God’s embracing grace.