Very few, if any, false teachers come into the church announcing their plans to lead Christ's sheep astray or proclaiming that they are there to overturn the gospel. In fact, history proves that false teachers are often some of the most charismatic individuals you will meet. They have a "way with words," able to sound mostly orthodox while denying, perhaps subtly, particular points that are necessary for faithfulness to our Lord. If they are confronted about this, they will often make a sweet-sounding appeal to unity, preying on people's inclination to avoid controversy whenever possible.
Of course, there is nothing wrong with speaking well or crafting eloquent sermons, and one of our highest callings as believers is to seek unity among the brethren (Ps. 133:1). But when people lead others astray using smooth talk, or they seek unity that does not have truth as its foundation, they are to be avoided, even cast out of the church (Rom. 16:17-18; 1 John 2:19). For the good of the body, false teaching cannot be tolerated.
Paul's warning about false teachers shows us how to identify them through signs other than the falsehood of the teaching itself. The first sign the Apostle gives is that false teachers serve "their own appetites." Literally, Paul says the teachers serve their bellies. He refers here, by way of metaphor, to a lifestyle that reflects indulgence and egocentrism. Christian teachers are not prohibited from enjoying nice things, but they are prohibited from living ostentatiously—from making their paycheck their chief end in their labor. As Paul teaches elsewhere, men fit to fill the office of elder will not be lovers of money (1 Tim. 3:1-7).
The second sign of false teachers is "smooth talk and flattery." This does not mean that pastors and teachers may not have gentle speech that people find pleasing, for Scripture says that "a gentle tongue is a tree of life" (Prov. 15:4). What the Apostle condemns is dishonest speech that is hidden by flattering comments and words that praise people for the sake of their approval and not because there is genuine sentiment behind it. False teachers use words to attract and retain others not for the sake of Christ but for their own sake. John Calvin comments, "The preachers of the gospel have also their courtesy and their pleasing manner, but joined with honesty, so that they neither soothe men with vain praises, nor flatter their vices: but impostors allure men by flattery, and spare and indulge their vices, that they may keep them attached to themselves."
When it comes to false teaching, what matters is not really the form of the words spoken but their content and the intent behind them. Sometimes truth must be presented with harsh words, but often it can be conveyed with gentleness. Similarly, words of praise do not have to be insincere. Whether we are teachers or not, let us seek to speak only the truth, and let us do so with the gentleness or firmness the occasion requires.