I read once about a seminary class that spent a semester searching the New Testament to discover which truth is emphasized more than any other. To their surprise they found that warnings against false teachers top the list, ahead of love or any other virtue. Jesus Himself warned (Matt. 7:15), “Beware of the false prophets, who come to you in sheep’s clothing, but inwardly are ravenous wolves.”
The metaphor pictures the deceptiveness and the self-centered destructiveness of false prophets. They fool the sheep into thinking that they are sheep, and thus gain access to the flock. But their aim is not to build up and care for the flock, but to ravage them for their own selfish purposes (see also, 2 Cor. 11:13-15; 2 Peter 2; and 1, 2, & 3 John).
Satan’s aim is never to build up or care for people! He always seeks to destroy (John 10:10; 1 Pet. 5:8). And he often uses as his agents men or women who pose as true believers to cause destruction in the church. They seem to know the Bible and teach the Bible, which gains them a hearing among those who profess to know Christ. But their teaching and their practices do not lead people toward godliness, but toward destruction.
“Thieves” and “robbers” have slightly different meanings. Thieves tend to use cunning and deception. They break into your house when you’re gone or are asleep and steal without your knowing it. Robbers are more aggressive. They hold you up at gunpoint and force you to give up your valuables. Be on the watch out.