“And, since it was necessary that His divine mission should be perpetuated to the end of time, He took to Himself disciples, trained by himself, and made them partakers of His own authority. And, when He had invoked upon them from Heaven the Spirit of Truth, He bade them go through the whole world and faithfully preach to all nations what He had taught and what He had commanded, so that by the profession of His doctrine and the observance of His laws, the human race might attain to holiness on earth and never-ending happiness in Heaven. In this wise, and on this principle, the Church was begotten. If we consider the chief end of His Church and the proximate efficient causes of salvation, it is undoubtedly spiritual; but in regard to those who constitute it, and to the things which lead to these spiritual gifts, it is external and necessarily visible. The Apostles received a mission to teach by visible and audible signs, and they discharged their mission only by words and acts which certainly appealed to the senses. So that their voices falling upon the ears of those who heard them begot faith in souls – ‘Faith cometh by hearing, and hearing by the words of Christ’ (Rom. x., 17). And faith itself – that is assent given to the first and supreme truth – though residing essentially in the intellect, must be manifested by outward profession – ‘For with the heart we believe unto justice, but with the mouth confession is made unto salvation’ (Rom. x., 10). In the same way in man, nothing is more internal than heavenly grace which begets sanctity, but the ordinary and chief means of obtaining grace are external: that is to say, the sacraments which are administered by men specially chosen for that purpose, by means of certain ordinances. Jesus Christ commanded His Apostles and their successors to the end of time to teach and rule the nations. He ordered the nations to accept their teaching and obey their authority. But his correlation of rights and duties in the Christian commonwealth not only could not have been made permanent, but could not even have been initiated except through the senses, which are of all things the messengers and interpreters. For this reason the Church is so often called in Holy Writ a body, and even the body of Christ – ‘Now you are the body of Christ’ (I Cor. xii., 27) – and precisely because it is a body is the Church visible: and because it is the body of Christ is it living and energizing, because by the infusion of His power Christ guards and sustains it, just as the vine gives nourishment and renders fruitful the branches united to it.” ~Pope Leo XIII, “Satis Cognitum”