At that time:
Jesus said to his disciples: Beware of false prophets, who come to you in the clothing of sheep, but inwardly they are ravenous wolves. By their fruits you shall know them. Do men gather grapes of thorns, or figs of thistles? Even so every good tree yieldeth good fruit, and the bad tree bad fruit. A good tree cannot yield bad fruit, neither can a bad tree yield good fruit. Every tree that yieldeth not good fruit, shall be cut down, and shall be cast into the fire. Wherefore by their fruits you shall know them. Not every man that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doeth the will of my Father who is in heaven, he shall enter into the kingdom of heaven.
Sermon XCVIII.
Beware of false prophets,
who come to you in the clothing of sheep,
but inwardly they are ravenous wolves.
—St. Matthew vii. 15.
A prophet is a teacher, and a teacher who assumes to have more than ordinary knowledge. He is one who claims to speak from authority, and demands a hearing on the score of his being inspired directly by the all-wise God, or as being commissioned to speak in the name of God. When such true teachers speak to us we are bound, of course, to listen to them, to receive their words with humility and obey them implicitly.
It is the way of God with men. We are taught all we know. Now, if all teachers were true teachers, all men would believe alike and there would be no error in the world. But because there have been and are many false teachers, there are many false religions and innumerable lies of all kinds which thousands believe to be truths. For one to be sure, therefore, that what he believes is true, he must not be simply content with the fact that he sincerely believes it, but he must know that his teacher is a true teacher.
Those who are not Catholics wonder how it is that we feel so certain of the truths of our faith. Their wonder would cease if they were to become Catholics, as it does happen with all converts; for then they would know, as we know, how it feels to be sure of one's teacher. That is our inestimable privilege and inexpressible joy—that we know our teacher is true, and that a false teacher is instantly detected, no matter how carefully and cunningly he has put on his sheep's clothing. The disguise is never thick enough to hide the wolf's teeth and claws.
I do not say that a Catholic may not be deceived and be misled by these wolves in sheep's clothings else our Lord would not have told us to beware of such, and the history of all heresies proves that many can be deceived by them. But that is their fault. They go out of the fold where all is light and clear, and where a wolf is found out in a moment, and they wander about in places and in company where there is no light of divine faith. To tell the truth, the false teacher finds his victims already misled and enticed away by their own passions and pride. He finds they have already begun to believe a lie, and he has only to encourage them in it. What do I mean by wandering outside the fold? I mean imitating the talk and following the example of those whose principles are false; who say: "Religion is a matter of choice"; "It does not matter what a man believes so long as he is good"; "Education is the business of the state"; "Religion has nothing to do with science"; and also immoral principles such as these: "A man cannot help his nature"; "A young man is expected to sow his wild oats"; "We are in the world and must go with it," and such like.