(17, 18) Even so every good tree. . . .--The two verses state nearly the same fact, but each presents a different aspect. First it is stated as a matter of practical experience, then the general fact is referred to a necessary law. If the tree is corrupt, i.e., rotten or decayed at the core, it cannot bring forth good fruit. If there is falseness in the teaching, or in the man, it will sooner or later show itself in his life, and then, even though we judge of the doctrine on other ground, we should cease to feel confidence in the guidance of the teacher.

Verse 17. - Matthew only. Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. The similarity between the fruit and the nature of the tree extends not only to the species, but also to the specimen. Good tree (δένδρον ἀγαθόν); intrinsically sound. Good fruit (καρποὺς καλούς); attractive in the eyes of men. As is the inner character of the tree, so is the obvious nature of the fruit. But a corrupt tree (τὸ δὲ σαπρὸν δένδρον); "the" picturing it. Corrupt; unsound, rotten, worthless (cf. Matthew 13:48); also in the moral world (Ephesians 4:29).

7:15-20 Nothing so much prevents men from entering the strait gate, and becoming true followers of Christ, as the carnal, soothing, flattering doctrines of those who oppose the truth. They may be known by the drift and effects of their doctrines. Some part of their temper and conduct is contrary to the mind of Christ. Those opinions come not from God that lead to sin.As is the tree, so is its fruit; if the tree is good, it will bring forth good fruit. The tree that brings forth good fruit, is good antecedent to the fruit it produces; it is first good, and then puts forth good fruit: it is not the fruit that makes the tree good, but makes it appear to be so; but it is the goodness of the tree that makes the fruit good. As a good man does, and will do good works, but his works do not make him a good man; he is so before he performs good works, or he would never be able to do them; these make him appear to be a good man: so a good preacher, that has an experimental knowledge of the doctrines of the Gospel, will deliver out sound doctrine, who is first made so by the gifts and graces of the Spirit of God; and by searching the Scriptures, and examining his doctrines by them, he will be known and appear to be a good minister of Jesus Christ, nourished up in the words of faith and good doctrine; and such a good minister of the Gospel, out of the good treasure of Gospel truths put into his earthen vessel, will bring forth, from time to time, good and excellent truths, to the edification and profit of those that hear: "but a corrupt tree bringeth forth evil fruit"; if the tree is corrupt, the fruit will be corrupt; and as is the preacher, so will be his doctrines: if he is a corrupt preacher, or a man of a corrupt mind, destitute of the truth, his preaching will be such as will tend to corrupt both the principles and practices of men; for such evil men and seducers, out of the evil treasure of false doctrines, which they have received into their judgments, will bring forth, either more secretly or openly, evil tenets in their ministry, which prove of bad consequence to the souls of men.