What does Matthew 7:15 mean?

The Sermon on the Mount (Matthew 5:1–2) has already provided several phrases now common in western culture. This verse provides another: the idea of a wolf in sheep's clothing. In previous verses, Jesus warned His followers they must enter the narrow gate and walk the hard road that leads to life (Matthew 7:13–14). Most people, He said, enter the wide gate and walk the easy path to destruction. Christ, Himself, is the narrow gate (John 10:9; 14:6) and the only way of salvation (Acts 4:12). The life of inner righteousness is harder than the shallow, performance-based hypocrisy modeled by so many (Matthew 5:20).

Here Jesus tells His followers to beware of false prophets. This can refer specifically to those who claim to be literal "prophets," or leaders. It also applies, in general, to those who make false religious claims. Such people may put on the appearance of innocence or brotherhood. In truth, they are as deceptive and dangerous as hungry wolves wearing sheep skins. Jewish people of Jesus' era would have grown up hearing stern warnings about listening to false prophets.

In this statement, Jesus is pointedly identifying those who oppose Him—those who lead people along the wide path of destruction—as false prophets hungry to devour an easily-led people. The most prominent examples of these, for Jesus' original audience, were the religious leaders of Israel. Those men will end up accusing Jesus of falseness and blasphemy. He is warning His listeners ahead of time that those men are the false prophets. They "devour" in the sense that they rely on the continued fear-driven submission of the Jewish people to maintain their own power and position (John 10:10).

This is the first half of a two-part lesson. After explaining how it's possible to be fooled by others, Jesus will go on to warn about the danger of fooling ourselves (Matthew 7:21).