And Jesus answering said to him: "And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it. And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose on earth, it shall be loosed also in heaven." (Matt. 16:18-19)
THE CHURCH OF CHRIST: Our Lord said that He would found a Church (one only), and that this Church could not be overcome. At the same time He elected Peter to be its foundation, and clearly chose the other apostles to be its pillars. Thus the twelve apostles, with Peter as their chief, were the foundation of the Church, upon which and into which all men, like so many stones, had to be built. The Church of Christ is, therefore, visible. She is formed of men, and governed by men, who are armed with the divine power of binding and loosing. The faithful owe obedience to this Church of Christ, and he who refuses to obey her is to be regarded as a heathen, who has no part in the kingdom of heaven.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]
(1899 Douay-Rheims Bible)