Fourth Lateran Council: 1215
http://www.papalencyclicals.net/Councils/ecuм12-2.htmConstitutions
1. Confession of Faith
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There is indeed one universal church of the faithful, outside of which nobody at all is saved. . .
Mystici Corporis
The Mystical Body of Christ, the Church
Pope Pius XII - 1943
http://www.papalencyclicals.net/pius12/p12mysti.htm10.
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Indeed no true and perfect human society can be conceived which is not governed by some supreme authority. Christ therefore must have given to His Church a supreme authority to which all Christians must render obedience. For this reason, as the unity of the faith is of necessity required for the unity of the church, inasmuch as it is the body of the faithful, so also for this same unity, inasmuch as the Church is a divinely constituted society, unity of government, which effects and involves unity of communion, is necessary jure divino. “The unity of the Church is manifested in the mutual connection or communication of its members, and likewise in the relation of all the members of the Church to one head” (St. Thomas, 2a 2ae, 9, xxxix., a. I). From this it is easy to see that men can fall away from the unity of the Church by schism, as well as by heresy. “We think that this difference exists between heresy and schism” (writes St. Jerome): “heresy has no perfect dogmatic teaching, whereas schism, through some Episcopal dissent, also separates from the Church” (S. Hieronymus, Comment. in Epist. ad Titum, cap. iii., v. 1011). In which judgment St. John Chrysostom concurs: “I say and protest (he writes) that it is as wrong to divide the Church as to fall into heresy” (Hom. xi., in Epist. ad Ephes., n. 5). Wherefore as no heresy can ever be justifiable, so in like manner there can be no justification for schism. “There is nothing more grievous than the sacrilege of schism….there can be no just necessity for destroying the unity of the Church” (S. Augustinus, Contra Epistolam Parmeniani, lib. ii., cap. ii., n. 25).
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59. What We have said concerning the “mystical Head” would indeed be incomplete if We were not at least briefly to touch on this saying of the same Apostle: “Christ is the Head of the Church: he is the Savior of his Body.” For in these words we have the final reason why the Body of the Church is given the name of Christ, namely, that Christ is the Divine Savior of this Body. The Samaritans were right in proclaiming Him “Savior of the world”; for indeed He most certainly is to be called the “Savior of all men,” even though we must add with Paul: “especially of the faithful, since, before all others, He has purchased with His Blood His members who constitute the Church.
St. Cyril
Catechetical Lecture 5
Of Faith
http://www.newadvent.org/fathers/310105.htm1. How great a dignity the Lord bestows on you in transferring you from the order of Catechumens to that of the Faithful, the Apostle Paul shows, when he affirms, God is faithful, by Whom you were called into the fellowship of His Son Jesus Christ. 1 Corinthians 1:9 For since God is called Faithful, thou also in receiving this title receive a great dignity. For as God is called Good, and Just, and Almighty, and Maker of the Universe, so is He also called Faithful. Consider therefore to what a dignity you are rising, seeing you are to become partaker of a title of God.
St. John Chrysostom
Homily 25 on the Gospel of John
http://www.newadvent.org/fathers/240125.htm3.
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What advantages it to be bound by the ties of earthly family, if we are not joined by those of the spiritual? What profits nearness of kin on earth, if we are to be strangers in heaven? For the Catechumen is a stranger to the Faithful. He has not the same Head, he has not the same Father, he has not the same City, nor Food, nor Raiment, nor Table, nor House, but all are different; all are on earth to the former, to the latter all are in heaven. One has Christ for his King; the other, sin and the devil; the food of one is Christ, of the other, that meat which decays and perishes; one has worms' work for his raiment, the other the Lord of angels; heaven is the city of one, earth of the other. Since then we have nothing in common, in what, tell me, shall we hold communion? Did we remove the same pangs, did we come forth from the same womb? This has nothing to do with that most perfect relationship. Let us then give diligence that we may become citizens of the city which is above. How long do we tarry over the border, when we ought to reclaim our ancient country? We risk no common danger; for if it should come to pass, (which God forbid!) that through the sudden arrival of death we depart hence uninitiated, though we have ten thousand virtues, our portion will be no other than hell, and the venomous worm, and fire unquenchable, and bonds indissoluble.
St. Leo the Great
Sermon 26
http://www.newadvent.org/fathers/360326.htmII. Christians are essentially participators in the nativity of Christ
Although, therefore, that infancy, which the majesty of God's Son did not disdain, reached mature manhood by the growth of years and, when the triumph of His passion and resurrection was completed, all the actions of humility which were undertaken for us ceased, yet today's festival renews for us the holy childhood of Jesus born of the Virgin Mary: and in adoring the birth of our Saviour, we find we are celebrating the commencement of our own life. For the birth of Christ is the source of life for Christian folk, and the birthday of the Head is the birthday of the body. Although every individual that is called has his own order, and all the sons of the Church are separated from one another by intervals of time, yet as the entire body of the faithful being born in the font of baptism is crucified with Christ in His passion, raised again in His resurrection, and placed at the Father's right hand in His ascension, so with Him are they born in this nativity. For any believer in whatever part of the world that is re-born in Christ, quits the old paths of his original nature and passes into a new man by being re-born; and no longer is he reckoned of his earthly father's stock but among the seed of the Saviour, Who became the Son of man in order that we might have the power to be the sons of God.
St. Hilary of Poitiers
On the Trinity (Book VIII)
http://www.newadvent.org/fathers/index.html7. For as to those whose soul and heart were one, I ask whether they were one through faith in God? Yes, assuredly, through faith, for through this the soul and heart of all were one. Again I ask, is the faith one or is there a second faith? One undoubtedly, and that on the authority of the Apostle himself, who proclaims one faith even as one Lord, and one baptism, and one hope, and one God. Ephesians 4:4-5 If then it is through faith, that is, through the nature of one faith, that all are one, how is it that you do not understand a natural unity in the case of those who through the nature of one faith are one? For all were born again to innocence, to immortality, to the knowledge of God, to the faith of hope. And if these things cannot differ within themselves because there is both one hope and one God, as also there is one Lord and one baptism of regeneration; if these things are one rather by agreement than by nature, ascribe a unity of will to those also who have been born again into them. If, however, they have been begotten again into the nature of one life and eternity, then, inasmuch as their soul and heart are one, the unity of will fails to account for their case who are one by regeneration into the same nature.
8. These are not our own conjectures which we offer, nor do we falsely put together any of these things in order to deceive the ears of our hearers by perverting the meaning of words; but holding fast the form of sound teaching we know and preach the things which are true. For the Apostle shows that this unity of the faithful arises from the nature of the sacraments when he writes to the Galatians, For as many of you as were baptized into Christ did put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female; for you are all one in Christ Jesus. Galatians 3:27-28 That these are one amid so great diversities of race, condition, sex — is it from an agreement of will or from the unity of the sacrament, since these have one baptism and have all put on one Christ? What, therefore, will a concord of minds avail here when they are one in that they have put on one Christ through the nature of one baptism?
St. Thomas Aquinas
Summa Thelogica
First Part
Question 21.
Article 1.
http://www.newadvent.org/summa/5021.htm#article1'
I answer that, When a man enters the Church by Baptism, he is admitted to two things, viz. the body of the faithful and the participation of the sacraments: and this latter presupposes the former, since the faithful are united together in the participation of the sacraments.
St. Ambrose
On Baptism: A Catechetical Instruction
http://www.lectionarycentral.com/trinity12/Ambrose.html1.
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I shall now begin to instruct you on the sacrament you have received; of whose nature it was not fitting to speak to you before this: for in the Christian what comes first is faith. And at Rome for this reason those who have been baptized are called the faithful (fideles).