"Beware of false prophets, who come to you in sheep's clothing, but underneath are ravenous wolves By their fruits you will know them. Do people pick grapes from thornbushes, or figs from thistles? Just so, every good tree bears good fruit, and a rotten tree bears bad fruit. A good tree cannot bear bad fruit, nor can a rotten tree bear good fruit. Every tree that does not bear good fruit will be cut down and thrown into the fire. So by their fruits you will know them. (Mt 7:15-20)
Prophets were called by God to reveal God to the people. They were speaking for God. They set the mind of God among people. They were not foretellers rather they were forth-tellers. They were not speaking before hand what was to happen (this was also done in some cases but not always) they were telling strongly to the people the plan of God the mind of God the demands of God.
So, false prophets were wolves in sheep clothing. Sheep is suppose to be a harmless creature. It is not only harmless but also it cannot save itself, help itself. It always needed someone to care for it and defend it and lead it through. Here the false prophets move about like the sheep among sheep (people of Israel) but they are wolves. Wolves are the real enemies of the sheep. False prophets are the real enemies of the people.
The false prophets are known by their fruits. Fruits of the trees reveal the tree. Here Jesus enters into a moral statement (Good tree and bad tree). But Jesus very specific about the prophets and he is not judging them rather he is warning his disciples to see the fruits of the trees (actions of the prophets). It is this that will help the people to find out the true prophets from the false ones.
