But some one will ask, How is it then, that certain excellent persons, and of position in the Church, are often permitted by God to preach novel doctrines to Catholics? A proper question, certainly, and one which ought to be very carefully and fully dealt with, but answered at the same time, not in reliance upon one's own ability, but by the authority of the divine Law, and by appeal to the Church's determination. Let us listen, then, to Holy Moses, and let him teach us why learned men, and such as because of their knowledge are even called Prophets by the apostle, are sometimes permitted to put forth novel doctrines, which the Old Testament is wont, by way of allegory, to call “strange gods,” forasmuch as heretics pay the same sort of reverence to their notions that the Gentiles do to their gods.
Blessed Moses, then, writes thus in Deuteronomy: “If there arise among you a prophet or a dreamer of dreams,” that is, one holding office as a Doctor in the Church, who is believed by his disciples or auditors to teach by revelation: well—what follows? “and gives you a sign or a wonder, and the sign or the wonder come to pass whereof he spoke,”— he is pointing to some eminent doctor, whose learning is such that his followers believe him not only to know things human, but, moreover, to foreknow things superhuman, such as, their disciples commonly boast, were Valentinus, Donatus, Photinus, Apollinaris, and the rest of that sort! What next? “And shall say to you, Let us go after other gods, whom you know not, and serve them.” What are those other gods but strange errors which you know not, that is, new and such as were never heard of before? “And let us serve them;” that is, “Let us believe them, follow them.” What last? “You shall not hearken to the words of that prophet or dreamer of dreams.” And why, I pray you, does not God forbid to be taught what God forbids to be heard? “For the Lord, your God, tries you, to know whether you love Him with all your heart and with all your soul.” The reason is clearer than day why Divine Providence sometimes permits certain doctors of the Churches to preach new doctrines— “That the Lord your God may try you;” he says. And assuredly it is a great trial when one whom you believe to be a prophet, a disciple of prophets, a doctor and defender of the truth, whom you have folded to your breast with the utmost veneration and love, when such a one of a sudden secretly and furtively brings in noxious errors, which you can neither quickly detect, being held by the prestige of former authority, nor lightly think it right to condemn, being prevented by affection for your old master.
-- St. Vincent of Lerins, The Commonitory, 10