Do not think it is the obvious that we can now who is a false teacher/prophet, it is those who profess to be believers who can lead you astray. Mat_7:15 “Beware of false prophets, who come to you in sheep’s clothing but inwardly are ravenous wolves.
This is an excellent sermon and exposition done by Pastor Vodie Baucham.
Please listen here :
Voddie Baucham
Though the culture at large has a problem with judging, Christians are not only allowed to do so, we are commanded to do so. In this portion of the Sermon on the Mount, Jesus informs us that we must learn to discern and expose false teaching and false teachers.
False prophets are not always easy to spot.D A Carson ” Warnings against false prophets are necessarily based on the conviction that not all prophets are true, that truth can be violated and that the gospels enemies usually conceal their hostility and try to pass them selves of as fellow believers” (Quote used by Voddie)
They will learn to use narrow gate language, they will learn to emulate, hard road living, they will learn to masquerade as small crowd people and they will learn to trick you into thinking that they are on the road that leads to life.
Here is why it is difficult to identify false prophets, …..number one, because of Biblical and theological illiteracy, if we don’t know the Bible, Doctrine or Theology it is virtually impossible to identify false prophets. That’s also why we are allergic to those who identify false prophets, it makes us uncomfortable. … (Why ? listen to the sermon 
Though the culture at large has a problem with judging, Christians are not only allowed to do so, we are commanded to do so. In this portion of the Sermon on the Mount, Jesus informs us that we must learn to discern and expose false teaching and false teachers.
Romans 1:26-32
26 For this reason God gave them up to vile passions. For even their women exchanged the natural use for what is against nature. 27 Likewise also the men, leaving the natural use of the woman, burned in their lust for one another, men with men committing what is shameful, and receiving in themselves the penalty of their error which was due.
28 And even as they did not like to retain God in their knowledge, God gave them over to a debased mind, to do those things which are not fitting; 29 being filled with all unrighteousness, sexual immorality,[a] wickedness, covetousness, maliciousness; full of envy, murder, strife, deceit, evil-mindedness; they are whisperers, 30 backbiters, haters of God, violent, proud, boasters, inventors of evil things, disobedient to parents, 31 undiscerning, untrustworthy, unloving, unforgiving,[b]unmerciful; 32 who, knowing the righteous judgment of God, that those who practice such things are deserving of death, not only do the same but also approve of those who practice them.
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