Ver. 17 Even so every good tree bringeth forth good fruit
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.
Read Matthew 7:17