Matthew 7:16 - Albert Barnes' Notes on the Bible

Ye shall know them by their fruits - The Saviour gives the proper test of their character. People do not judge of a tree by its leaves, or bark, or flowers, but by the fruit which it bears. The flowers may be beautiful and fragrant, the foliage thick and green; but these are merely ornamental. It is the “fruit” that is of chief service to man; and he forms his opinion of the nature and value of the tree by that fruit. So of pretensions to religion. The profession may be fair; but the “conduct” - the fruit - is to determine the nature of the principles.