(20) Ye shall know them.--As before, in Matthew 7:16, the word is one which implies knowledge that is full, clear, decisive--such as that to which St. Paul looks forward in the life to come (1Corinthians 13:12).

Verse 20. - (Ver. 16, note.) Wherefore by their fruits ye shall know them. Wherefore (ἄραγε). Ver. 16a is restated, but now in "rigorous logical inference" (Winer, § 53:8. a) from vers. 16b - 18. Since it is a certainty that fruit is the result of inner nature, you shall from these men's fruits fully learn their true character.

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.Wherefore by their fruits ye shall know them. This is the conclusion of the whole, and a repetition of what is before said, the more to fix the rule of judgment upon their minds, and engage them to try men by their doctrines, and their doctrines by the standard of the Scriptures, and not believe every spirit; for with some care and diligence such persons may be detected, and the malignant influence of their ministry be prevented. The sum of the whole is, that ordinarily, and generally speaking, as men are, so are the doctrines they preach, and by them they may be known, and judged to be what they are. Christ here, and in the preceding verses, is speaking not of men of bad lives and conversations, who take upon them to teach others; for there is not so much reason to caution good men against these; they are easily detected, and generally discarded; but of men that put on sheep's clothing, who pretended to much holiness of life and conversation, and strictness of religion; and under that disguise delivered out the most corrupt and unwholesome doctrines; which tended greatly to depreciate him and his grace, and to do damage to the souls of men.