Charles Ellicott Commentary Matthew 7:16

"By their fruits ye shall know them. Do [men] gather grapes of thorns, or figs of thistles?" — Matthew 7:16 (ASV)

You will know them by their fruits—The question, "What are the fruits?" is not directly answered. Those who attach most importance to the ethical side of religion see in them the practical outcome of doctrine in life, character, and deeds. Others, who live in a constant dread of heresy, dwell on doctrines rather than acts as the "fruits" by which we are to discern the false teachers and the true. Good works, they say, may be merely the sheep’s clothing that hides the heretical wolf.

The analogy of scriptural language, and even that of most theologians—the familiar phrases which speak of good works as the fruits of faith and the like—are, it is believed, entirely in favor of the former view. Still more decisive are the fruits meet for repentance (Matthew 3:8). We are to judge the teaching of those who claim authority by the degree to which, in the long run, it promotes purity, peace, and holiness.