Jesus was not polite to false teachers...

Many Christians today are greatly concerned about the rising influences of communism, humanism, secularism, and social injustice. Yet those evils, great as they are, do not together pose the threat to Christianity that false shepherds and pastors do. Throughout the history of redemption, the greatest threat to God’s truth and God’s work has been false prophets and teachers, because they propose to speak in His name. That is why the Lord’s most scathing denunciations were reserved for the false teachers of Israel, who claimed to speak and act for God but were liars.

Yet for some reason, evangelical Christianity is often hesitant to confront false teachers with the seriousness and severity that Jesus and the apostles did, and that the godly prophets before them had done. Today, more than at any time in modern history and perhaps more than at any time in the history of the church, pagan religions and cults are seriously encroaching on societies that for centuries have been nominally Christian. Even within the church, many ideas, teachings, and philosophies that are little more than thinly veiled paganism have become popular and influential.

As in ancient Israel, the further God’s people move away from the foundation of His Word, the more false religion flourishes in the world and even in their own midst. At no time have Christians had greater need to be discerning. They need to recognize and respect true godly shepherds who feed them God’s Word and build them up in the faith, and they also must recognize and denounce those who twist and undermine God’s Word, who corrupt the church and who lead lost people still further away from God’s truth and from salvation.

- John MacArthur (online source)