The doctrine which the Saviour left us, and the laws which He prescribed were vastly different from the teachings of men. Guiding, saving words of a Shepherd to his flock, they engendered safety, comfort, peace. Free from error or mistake, sealed with the seal of Heaven, holding out a promise of future glory, they exhaled the perfumes of the eternal city, they told of mansions not built with hands. And since this immaculate doctrine, given for the souls of men, was to last till the end of time, there was need that it should be shielded against the assaults of the world and protected from the influence of our changing human teachings. It could not be corrected, because it contained no mistakes; it could not be changed or altered, because it came from the changeless God; it could have no substitute from the part of men or creatures of any kind, because it was given by Him who alone was the way, the truth, and the life. Consequently the truths which the Saviour declared to the world as the only means by which we can be saved, were at once infallible in themselves, and so provided for that no human agency, no lapse of years or revolutions of time and place should ever be able to infringe on their eternal, changeless character. It was to preserve these truths in their integrity and freshness that He founded His unerring Church and committed to it the office of custodian and expounder, under the guidance of His Holy Spirit, of all He had revealed for the salvation of human kind. Hence to hear our Shepherd’s voice, to understand what He says to us, to know what we must do to obey His laws and save our souls, we need but listen to the voice of His Church. Before it was established He declared that He should build His Church upon a rock, and that no enemy, or group of enemies, not even the gates of hell should ever prevail against it.(27) He established the Church as His mouthpiece, and He said to the little band that constituted it in the beginning, “he that heareth you, heareth me, and he that heareth me, heareth Him that sent me;”(28) and, as if to emphasize this declaration, He added that any one who would not hear and obey the Church should be considered as a heathen and a publican—types of all that was bad.(29) The Church, therefore, is the oracle of God, it is His mouthpiece; it possesses and guards the only revelation which God has made to His rational creatures; it alone has the words of eternal life.