The primacy is in exercise when the teaching of the Universal Church is the motive and the end, and then only when the matter of the teaching is of faith and morals. In such acts the promise made to Peter is fulfilled, and a divine assistance guides and guards the head of the Church from error. The definition declares that he then is possessed of the infallibility with which our Saviour willed to endow his Church.
8. Now it is to be here remembered that all Catholics believe the Church to be infallible in faith and morals—that is, that the Church is so divinely guarded that it never departs from the divine tradition of revealed truth. This all Catholics believe; no one who denies it is a Catholic. Whosoever doubts it ceases to be a Catholic. But this doctrine has never been defined. It needs no definition. No definition could make it more certain or more universal in its reception. Why then was the infallibility of the head of the Church defined? Simply because it had been denied by some; and, lest it should be denied by more, through the apparent impunity granted to the denial, the definition has put it beyond doubt. No one who denies it now is a Catholic; they who doubted it before were in an error which was at least proximate to heresy. They who doubt it now cannot be cleared of formal resistance to the divine authority of the Church. Such is the meaning of the words, "If any
