"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. . ."
"He is the true and genuine Catholic who loves the truth of God, who loves the Church, who loves the Body of Christ, who esteems divine religion and the Catholic Faith above every thing, above the authority, above the regard, above the genius, above the eloquence, above the philosophy, of every man whatsoever; who sets light by all of these, and continuing steadfast and established in the faith, resolves that he will believe that, and that only, which he is sure the Catholic Church has held universally and from ancient time; but that whatsoever new and unheard-of doctrine he shall find to have been furtively introduced by some one or another, besides that of all, or contrary to that of all the saints, this, he will understand, does not pertain to religion, but is permitted as a trial, being instructed especially by the words of the blessed Apostle Paul, who writes thus in his first Epistle to the Corinthians, "There must needs be heresies, that they who are approved may be made manifest among you:" as though he should say, This is the reason why the authors of Heresies are not immediately rooted up by God, namely, that they who are approved may be made manifest; that is, that it may be apparent of each individual, how tenacious and faithful and steadfast he is in his love of the Catholic faith."
St. Vincent of Lerins Commonitory