St Vincent of Lerins (434 AD) penned excellent simple advice that will help us determine what is the complete genuine Christian faith that Christ and His Apostles handed down. “Catholic” is his letters is not referring to “Roman Catholicism” but refers to the “universal” Christian church, the one unified church, where every bishop was invested with the authority of Christ equally and held to the same doctrines. Rome had not yet departed from the unified Orthodox Christian faith with their innovations.
Vincent of Lerins : “The Commonitories”
“But here some one perhaps will ask, Since the canon of Scripture is complete, and sufficient of itself for everything, and more than sufficient, what need is there to join with it the authority of the Church’s interpretation? For this reason, — because, owing to the depth of Holy Scripture, all do not accept it in one and the same sense, but one understands its words in one way, another in another; so that it seems to be capable of as many interpretations as there are interpreters. For Novatian expounds it one way, Sabellius another, Donatus another, Arius, Eunomius, Macedonius, another, Photinus, Apollinaris, Priscillian, another, Iovinian, Pelagius, Celestius, another, lastly, Nestorius another. Therefore, it is very necessary, on account of so great intricacies of such various error, that the rule for the right understanding of the prophets and apostles should be framed in accordance with the standard of Ecclesiastical and catholic interpretation. . .
Moreover, in the catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all. For that is truly and in the strictest sense “catholic,” which, as the name itself and the reason of the thing declare, comprehends all universally. This rule we shall observe if we follow universality, antiquity, consent.
We shall follow universality if we confess that one faith to be true, which the whole Church throughout the world confesses; antiquity, if we in no wise depart from those interpretations which it is manifest were notoriously held by our holy ancestors and fathers; consent, in like manner, if in antiquity itself we adhere to the consentient definitions and determinations of all, or at the least of almost all priests and doctors. . . .
. . . . What then will a catholic Christian do, if a small portion of the Church have cut itself off from the communion of the universal faith? What, surely, but prefer the soundness of the whole body to the unsoundness of a pestilent and corrupt member? What, if some novel contagion seek to infect not merely an insignificant portion of the Church, but the whole? Then it will be his care to cleave to antiquity, which at this day cannot possibly be seduced by any fraud of novelty.
But what, if in antiquity itself there be found error on the part of two or three men, or at any rate of a city or even of a province? Then it will be his care by all means, to prefer the decrees, if such there be, of an ancient General Council to the rashness and ignorance of a few. But what, if some error should spring up on which no such decree is found to bear? Then he must collate and consult and interrogate the opinions of the ancients, of those, namely, who, though living in divers times and places, yet continuing in the communion and faith of the one catholic Church, stand forth acknowledged and approved authorities: and whatsoever he shall ascertain to have been held, written, taught, not by one or two of these only, but by all, equally, with one consent, openly, frequently, persistently, that he must understand that he himself also is to believe without any doubt or hesitation. . . .
. . . But some one will say. perhaps, Shall there, then, be no progress in Christ’s Church? Certainly; all possible progress. For what being is there, so envious of men, so full of hatred to God, who would seek to forbid it? Yet on condition that it be real progress, not alteration of the faith. For progress requires that the subject be enlarged in itself, alteration, that it be transformed into something else. The intelligence, then, the knowledge, the wisdom, as well of individuals as of all, as well of one man as of the whole Church, ought, in the course of ages and centuries, to increase and make much and vigorous progress; but yet only in its own kind; that is to say, in the same doctrine, in the same sense, and in the same meaning. . . .
. . . But let us return to the apostle. “O Timothy,” he says, “Guard the deposit,; shunning profane novelties of words. ” “Shun them as you would a viper, as you would a scorpion, as you would a basilisk, lest they smite you not only with their touch, but I even with their eyes and breath.” What is “to shun” ? Not even to eat with a person of this sort What is “shun”? “If anyone,” says St. John, “come to you and bring not this doctrine. What doctrine ? What but the catholic and universal doctrine, which has continued one and the same through the several successions of ages by the uncorrupt tradition of the truth and so will continue for ever . . .
. . . Here, possibly, some one may ask, Do heretics also appeal to Scripture ? They do indeed, and with a vengeance; for you may see them scamper through every single book of Holy Scripture, — through the books of Moses, the books of Kings, the Psalms, the Epistles, the Gospels, the Prophets. Whether among their own people, or among strangers, in private or in public, in speaking or in writing, at convivial meetings, or in the streets, hardly ever do they bring forward anything of their own which they do not endeavor to shelter under words of Scripture. Read the works of Paul of Samosata, of Priscillian, of Eunomius, of Jovinian, and the rest of those pests, and you will see an infinite heap of instances, hardly a single page, which does not bristle with plausible quotations from the New Testament or the Old. . .
. . . But some one will say, What proof have we that the Devil is wont to appeal to Holy Scripture? Let him read the Gospels wherein it is written, “Then the Devil took Him (the Lord the Savior) and set Him upon a pinnacle of the Temple, and said unto Him: If thou be the Son of God, cast thyself down, for it is written, He shall give His angels charge concerning thee, that they may keep thee in all thy ways: In their hands they shall bear thee up, lest perchance thou dash thy foot against a stone.” What sort of treatment must men, insignificant wretches that they are, look for at the hands of him who assailed even the Lord of Glory with quotations from Scripture? “If thou be the Son of God,” saith be, “cast the, self down.” Wherefore? “For,” saith he, “it is written.” It behooves us to pay special attention to this passage and bear it in mind, that, warned by so important an instance of Evangelical authority, we may be assured beyond doubt, when we find people alleging passages from the Apostles or Prophets against the catholic Faith, that the Devil speaks through their mouths. For as then the Head spoke to the Head, so now also the members speak to the members, the members of the Devil to the members of Christ, misbelievers to believers, sacrilegious to religious, in one word, Heretics to Catholics. . .
. . . But it will be said, If the words, the sentiments, the promises of Scripture, are appealed to by the Devil and his disciples, of whom some are false apostles, some false prophets and false teachers, and all without exception heretics, what are Catholics and the sons of Mother Church to do? How are they to distinguish truth from falsehood in the sacred Scriptures? They must be very careful to pursue that course which, in the beginning of this Commonitory, we said that holy and learned men had commended to us, that is to say, they must interpret the sacred Canon according to the traditions of the Universal Church and in keeping with the rules of catholic doctrine, in which catholic and Universal Church, moreover, they must follow universality, antiquity, consent. And if at any time a part opposes itself to the whole, novelty to antiquity, the dissent of one or a few who are in error to the consent of all or at all events of the great majority of Catholics, then they must prefer the soundness of the whole to the corruption of a part; in which same whole they must prefer the religion of antiquity to the profaneness of novelty; and in antiquity itself in like manner, to the temerity of one or of a very few they must prefer, first of all, the general decrees, if such there be, of a Universal Council, or if there be no such, then, what is next best, they must follow the consentient belief of many and great masters. Which rule having been faithfully, soberly, and scrupulously observed, we shall with little difficulty detect the noxious errors of heretics as they arise.”