The Church has defined that heretics are the gates of Hell which Our Lord mentioned in Matthew 16!
Pope Vigilius, Second Council of Constantinople, 553: “… we bear in mind what was promised about the holy Church and Him who said the gates of Hell will not prevail against it (by these we understand the death-dealing tongues of heretics)…”[1]
Pope St. Leo IX, Sept. 2, 1053: “The holy Church built upon a rock, that is Christ, and upon Peter… because by the gates of Hell, that is, by the disputations of heretics which lead the vain to destruction, it would never be overcome.”[2]
St. Thomas Aquinas (+1262): “Wisdom may fill the hearts of the faithful, and put to silence the dread folly of heretics, fittingly referred to as the gates of Hell.”[3] (Intro. To Catena Aurea.)
Notice that heretics are the gates of Hell. Heretics are not members of the Church.
[1] Decrees of the Ecumenical Councils, Vol. 1, p. 113.
[2] Denzinger, The Sources of Catholic Dogma, B. Herder Book. Co., Thirtieth Edition, 1957, no. 351.
[3] The Sunday Sermons of the Great Fathers, Regnery, Co: Chicago, IL, 1963, Vol. 1, pp. xxiv.
