The catholic visible form of the Church, as pointed out above, is indicated in the papacy. But in what relation does the latter stand to the interior catholicity of the Church? In order to find the right answer to this decisive question, we must first more exactly define in what sense the papacy must be regarded as the bond of the historical unity of the Church. It must be so regarded, precisely in so far as the primacy has been instituted for the special end of preserving the faith incorrupt. According to the teaching of the Fathers of the Church, Peter is the Church's foundation of rock, in virtue of his faith. [Footnote 26] By this, of course, is not meant the personal confession of the Apostle Peter, but the object-matter of the same, the contents of the faith to be preached by Peter and his successors. Peter, says Leo the Great, is called by Christ the Rock, on account of the solidity of the faith which he was to preach, _pro soliditate fidei quam erat praedicaturus_. [Footnote 27 ] This is not the place to develop further in what way the papacy proves itself in act the cement of the unity of faith. We shall speak of that later. It is enough for our purpose, in the meanwhile, to take note of the judgment of the ancient Church. According to the doctrine of the Fathers of the Church, the fundamental significance which the papacy has for the Church, rests upon a relation of dependence between her faith and the faith of Peter, including by consequence that of his successors. In this sense St. Hilarius distinctly calls the faith of the Apostle Peter the foundation of the Church. [Footnote 28] The same view is found in St. Ambrose, [Footnote 29] expressed in nearly the same words. But if Peter is the Church's foundation of rock precisely through his faith, that mutual relation between the inner catholicity of the Church and the papacy is no longer doubtful. For that the Church, according to her inward essence, verifies herself as the Catholic Church, she owes precisely to her faith, as likewise, on the other side, her catholic visible form is conditioned by the outward profession of the same faith. Consequently, the papacy as guardian of the unity of faith, stands also in a necessary connection with the inner being of the Church. Here then we have the uniting member we have been seeking between inward and outward catholicity, the essence and the manifestation of the Church. _In so far as the historical connection with Peter must be conceived as a bond of faith, in this same connection or in the form of Catholicism, the true Church, even as to her inner being, comes historically into visible manifestation._ [Footnote 26: See the relevant passages from the fathers in Ballerini, _De vi ac rations primatus Rom. Pont._, cap. xii., § 1, No. 1. ] [Footnote 27: Serm. 62.] [Footnote 28: _De Trin_., vi. 37. ] [Footnote 29: _De Incarn_., cap. 5. ]