"The innovators themselves do not deny that the Roman Church was the first which Jesus Christ founded. However, they say that it was the true Church until the fifth century, or until it fell away, because it had been corrupted by the Catholics. But how could that Church fall which St. Paul calls the "pillar and ground of truth" [1 Timothy 3:15]? No, the Church has not failed. The truth is, that all the false churches, which have separated from the Roman Church, have fallen away and erred. "
"To convince all heretical sects of their error, there is no way more certain and safe than to show that our Catholic Church has been the first one founded by Jesus Christ. For, this being established, it is proved beyond all doubt that ours is the only true Church and that all the others which have left it and separated are certainly in error. But, pressed by this argument, the innovators have invented an answer. They say that the visible Church has failed, but not the invisible Church. But these doctrines are diametrically opposed to the Gospel. "
~St. Alphonsus Ligouri