"The practice of the Church has always been the same, as is shown by the unanimous teaching of the Fathers, who were wont to hold as outside Catholic communion, and alien to the Church, whoever would recede in the least degree from any point of doctrine proposed by her authoritative Magisterium. Epiphanius, Augustine, Theodore drew up a long list of the heresies of their times. St. Augustine notes that other heresies may spring up, to a single one of which, should any one give his assent, he is by the very fact cut off from Catholic unity. 'No one who merely disbelieves in all (these heresies) can for that reason regard himself as a Catholic or call himself one. For there may be or may arise some other heresies, which are not set out in this work of ours, and, if any one holds to one single one of these he is not a Catholic' (S. Augustinus, De Haeresibus, n. 88)….The need of this Divinely instituted means for the preservation of unity, about which we speak is urged by St. Paul in his epistle to the Ephesians. In this he first admonishes them to preserve with every care concord of minds: "Solicitous to keep the unity of the Spirit in the bond of peace" (Eph. iv., 3, et seq.). And as souls cannot be perfectly united in charity unless minds agree in faith, he wishes all to hold the same faith: "One Lord, one faith," and this so perfectly one as to prevent all danger of error." -Pope Leo XIII, Encyclical Satis Cognitum, #9, 1896 (infallible).