The following is an excerpt from The MacArthur New Testament Commentary on Matthew 7.

You will know them by their fruits. Grapes are not gathered from thorn bushes, nor figs from thistles, are they? Even so, every good tree bears good fruit; but the bad tree bears bad fruit. A good tree cannot produce bad fruit, nor can a bad tree produce good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. So then, you will know them by their fruits. (Matthew 7:16–20)

After warning about false prophets, Jesus tells us what to watch for in identifying them. Because they are so extremely deceptive and dangerous ravenous spiritual and moral wolves in sheep’s clothing-the Lord would hardly have left us without means of determining who they are.

Jesus assures us that we will know them by their fruits. A fruit tree may be beautiful, decorative, and offer pleasant shade in the summer. But its primary purpose is to bear fruit, and it is therefore judged by what it produces and not by how it looks. (That understanding is the key to interpreting John 15 properly.)

Similarly a prophet-used in this passage in the broadest sense of one who speaks for God-is judged by his life, not simply by his appearance or his words. The kind of person he really is cannot help being revealed. Some false prophets are noticeably spurious and only the most gullible person would be taken in by them. Others conceal their true nature with remarkable skill, and only careful observation will expose them for what they are. But there is a true assurance in the statement you will know them. There is no need to be deceived if we look closely.

It is the cleverly deceptive false prophet that Jesus is speaking about here. No one needs help in deciding that a tree is bad if it bears shriveled, discolored, and obviously rotten fruit-or no fruit at all. It is the tree that appears to bear good fruit, but does not, that is deceptive.

It is possible for grapes to be stuck on thorn bushes and for figs to be stuck on thistles. From a distance they might appear to be growing on real fruit trees. Because the fruit is genuine, naive persons might conclude that the tree itself also has to be genuine.

It is possible for real Christians to be taken in by false prophets. When believers are careless about study of and obedience to the Word, lazy about prayer, and uncritical about the things of God, it is easy for them to be deceived by someone who pretends to be orthodox-especially if he is pleasant, positive, and permissive. When that happens, they are in danger of becoming grapes on thorn bushes and figs on thistles. Satan loves to use God’s own people to promote his evil work, seeking, if it were possible, even to snatch them from their heavenly Father (Matt. 24:24).

It is also possible for a tree itself to bear fruit that is colorful, well formed, and attractive, but which is bitter, distasteful, and even poisonous. That kind of bad tree with its bad fruit is much harder to judge than thorn bushes that have grapes on them or thistles that have figs on them. In the second case, both the tree and the fruit appear to be genuine. What it bears has to be examined carefully to determine if it is good fruit or bad fruit. A mature believe who has developed discernment can spot the bad tree and bad fruit (Heb. 5:14).

Judging the fruit of false prophets, of course, is not nearly so easy as judging fruit in an orchard. But from Scripture we discover at least three primary tests we can apply in order to know. They are in the areas of character, creed, and converts.

Our Lord closes this potent section with an affirming repetition of verse 16, so then, you will know them by their fruits. Thus we are once again called to be discerning when listening to preachers who call us to the broad way that leads to death and hell.