“Beware of false prophets, who come to you in sheep’s clothing, but inwardly they are ravenous wolves. “You will know them by their fruits. Do men gather grapes from thorn bushes or figs from thistles? “Even so, every good tree bears good fruit, but a bad tree bears bad fruit. “A good tree cannot bear bad fruit, nor can a bad tree bear good fruit. “Every tree that does not bear good fruit is cut down and thrown into the fire. “Therefore by their fruits you will know them. (Mat 7:15-20 NKJ)
Jesus has just finished teaching about the narrow gate, the highway of holiness. Now he warns his hearers to beware of false prophets. The warning here is not so much about the heretic, but the hypocrites. The Pharisees were the main recipients of this sermon, with all their false teaching and hypocrisy. Jesus knows that they would try to persuade the people with their interpretation of Jesus’ teaching. Outwardly they appear godly (sheep), but inwardly they’re wolves.
Anybody can look as though they are Christian, but their fruit will be the proof. The fruit is determined by the root, and only the person that has deep roots in Jesus Christ can produce the fruit that Jesus expects.