Luke 6:44

For every tree is known by its own fruit
Good and bad preachers are known by their doctrines, the one being agreeable, the other disagreeable to the word of God; and good and bad men are known by their lives and conversations: the grace of God revealed to good men, and wrought in them, teaches them to live soberly, righteously, and godly; a holy life is the fruit of grace, and an evidence of it; and the wickedness that is in the heart of unregenerate men, and even the hypocrisy of formal professors, will show themselves in the common and ordinary course of their conversations:

for of thorns men do not gather figs, nor of a bramble bush gather
they grapes;
nor can they be expected from them: and no more can an unregenerate man perform good works, or bring forth: fruits of righteousness acceptable unto God; for these require a knowledge of his will, obedience to it, a principle of grace, love to God, faith in Christ, and a view to the glory of God; all which are wanting in such a person.