This infallibility, not only of the Roman Pontiff, but also of the local Church of Rome, was a central theme in the ecclesiology of some of the greatest Counter-Reformation theologians. Cardinal Hosius proposed this thesis in his polemic against Brentius.[33] John Driedo developed it magnificently.[34] St. Robert explained this teaching by saying that the Roman clergy and the Roman laity, as a corporate unit, could never fall away from the faith.[35] The Roman Church, as an individual local institution, can never fall away from the faith. Manifestly the same guarantee is given to no other local Church.It is interesting to note that during the prolonged vacancy of the Roman See the presbyters and the deacons of Rome wrote to St. Cyprian in such a way as to manifest their conviction that the faith of their own local Church, even during this interregnum, constituted a norm to which the faith of other local Churches was meant to conform.[36] The Roman Church could not possibly be the one with which all the other local congregations of Christendom must agree were it not endowed with a special infallibility. In order to be effective that infallibility must be acknowledged in a very practical manner by the other local units of the Church militant throughout the world.
Actually the infallibility of the Roman Church is much more than a mere theological opinion. The proposition that "the Church of the city of Rome can fall into error" is one of the theses of Peter de Osma, formally condemned by Pope Sixtus IV as erroneous and as containing manifest heresy.[37]
Msgr. Joseph Clifford Fenton was one of the most eminent theologians of 20th Century America. He was trained at the Angelicum in Rome and did his doctoral dissertation under the revered theologian, Father Reginald Garrigou-Lagrange, O.P. From 1944 to 1963, he was editor of the theological journal, the American Ecclesiastical Review. He also defended the doctrine "outside the Church there is no salvation," and upheld the traditional Papal Teaching on the Confessional State.