Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns or figs of thistles? Even so every good tree brings forth good fruit; but a corrupt tree brings forth evil fruit. A good tree cannot forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that brings not forth good fruit is cut down, and caste into fire [Matthew 7.15-19]