Ye shall know them by their fruits— That is, by the evil tendency of their doctrines, as well as by the immorality of their lives. Compare 1 John 4:1. 1 Corinthians 13:3. What follows seems to be a kind of proverb, and there occur in heathen authors many similar sayings. Several commentators are of opinion, that the fruits here referred to are rather the nature and tendency of the doctrine, than the actions of the false teacher's lives; but I rather think that our Lord here spoke of actions, which are often called fruits. Compare ch. Matthew 3:8 Matthew 21:43. John 15:2; John 15:5. Colossians 1:6 and see 2 Timothy 3:5; 2 Timothy 3:9. It will be objected, that bad men may teach good doctrines, and the worst have been known to do it in some instances. But to this I answer, that our Lord does not exhort his disciples to reject whatever such men taught; but only to be upon their guard against them, that they might not credit any thing merely on their authority.
Related Commentaries of Matthew 7:16
Matthew 7:16-20
16 Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles?
17 Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit.
18 A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit.
19 Every tree that bringeth not forth good fruit is hewn down, and cast into the fire.
20 Wherefore by their fruits ye shall know them.