"I say the Pope is the heir of the Ecumenical Hierarchy of the fourth century, as being, what I may call, heir by default. No one else claims or exercises its rights or its duties. Is it possible to consider the Patriarch of Moscow or of Constantinople, heir to the historical pretensions of St. Ambrose or St. Martin? Does any Anglican Bishop for the last 300 years recall to our minds the image of St. Basil? Well, then, has all that ecclesiastical power, which makes such a show in the Christian Empire, simply vanished, or, if not, where is it to be found?
I wish Protestants would throw themselves into our minds upon this point; I am not holding an argument with them; I am only wishing them to understand where we stand and how we look at things. There is this great difference of belief between us and them: they do not believe that Christ set up a visible society, or rather kingdom, for the propagation and maintenance of His religion, for a necessary home and a refuge for His people; but we do.
We know the kingdom is still on earth: where is it? If all that can be found of it is what can be discerned at Constantinople or Canterbury, I say, it has disappeared; and either there was a radical corruption of Christianity from the first, or Christianity came to an end, in proportion as the type of the Nicene Church faded out of the world: for all that we know of Christianity, in ancient history, as a concrete fact, is the Church of Athanasius and his fellow Bishops: it is nothing else historically but that bundle of phenomena, that combination of claims, prerogatives, and corresponding acts, some of which I have recounted above. There is no help for it then; we cannot take as much as we please, and no more, of an institution which has a monadic existence. We must either give up the belief in the Church as a divine institution altogether, or we must recognize it at this day in that communion of which the Pope is the head. With him alone and round about him are found the claims, the prerogatives, and duties which we identify with the kingdom set up by Christ. We must take things as they are; to believe in a Church, is to believe in the Pope. And thus this belief in the Pope and his attributes, which seems so monstrous to Protestants, is bound up with our being Catholics at all; as our Catholicism is bound up with our Christianity. There is nothing then of wanton opposition to the powers that be, no dinning of novelties in their startled ears in what is often unjustly called Ultramontane doctrine; there is no pernicious servility to the Pope in our admission of his pretensions."
Bl. John Henry Newman
Letter to the Duke of Norfolk