Matthew 7:17

Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but the corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Therefore by their fruits ye shall know them.

This teaching pertains primarily to the identification of false teachers whose true character is inevitably exposed by the results of their efforts. However cloaked with specious piety, however influential through personal charm, however marked by brilliant intellect or high educational attainment, or however distinguished in any other manner, false teachers are not to be trusted above the word of Christ. The teacher that divides and scatters the flock must be rejected. Evil fruits, or results, constitute certain and unmistakable identification with the "wolves" Jesus mentioned here.