(1) The bride of Christ cannot be defiled. She is inviolate and chaste. She knows one home only; in all modesty she keeps faithfully to one bridal chamber. It is she who preserves us for God, she who seals for the Kingdom the sons born to her. Whoever breaks with the Church and enters on an adulterous union cuts himself off from the promises made to the Church. He who turns his back on the Church of Christ will not come to the rewards of Christ; he is an alien, a world-ling, an enemy. You cannot have God for your Father if you no longer have the Church for your mother.
If there was any escape for anyone who was outside the Ark of Noah, there will be the same for one found outside the Church. The Lord warns us when He says: "He that is not with me is against me, and he that gathers not with me scatters" (Mt. 12:30). Whoever breaks the peace and harmony of Christ acts against Christ; whoever gathers elsewhere than in the Church scatters the Church of Christ. The Lord says "I and the Father are one" (Jn.10:30), and again, it is written of the Father, Son and Holy Spirit, "And the three are one" (1 Jn. 5:8). Dos anyone think, then that this oneness, which drives from God's stability and welded together after the heavenly pattern can be sundered in the Church and divided by the clash of discordant wills?
( St.Cyprian, in On the Unity of the Church )
(2) Therefore, in the order of the Creed, after the reference to “holy Church” comes reference to “forgiveness of sins.” For it is by this that the role of the Church on earth stands; it is by this that ‘what was lost and is found again’ (Lk.15:24) is not lost again. Now the gift of the baptism is, of course, an exception.
It is an antidote given to us against original sin, so that what is contracted by being born is removed by being born again, though it also takes away actual sins as well, whether of heart, word or deed. But, apart from this great remission – the beginning point of man’s renewal, in which all guilt, original and actual is washed away – the rest of life, after reaching the use of reason, no matter how resolutely we progress in virtue is not without the need for the forgiveness of sins.
This is so because the sons of God, as long as they live this mortal life, are in a conflict with death. And, although it is truly said of them, “As many as are led by the Spirit of God, they are the sons of God” (Rom.8:14), yet even as they are led by the Spirit of God and, as sons of God, advance toward God, they are also being led by their own spirits, so that, burdened by the corruptible body and under the influence of certain human feelings, they thus fall away and commit sin.
But it is a matter of proportion. Although every crime is a sin, not every sin is a crime. Thus we can say of the life of holy men, even while they exist in this moral state, that they are found without crime. “But if we say that we have no sin”, as the great apostle says,
“we deceive ourselves, and the truth is not in us.” (1 Jn.1:8)
Nevertheless, no matter how great our crimes, forgiveness for them should never be despaired of in holy church by those who truly repent, each in proportion to his sin. And, in the act of repentance, when a crime has been committed of such gravity as also to lead to exclusion of the sinner from the body of Christ, we should consider not so much the measure of time as the measure of sorrow. For, “a contrite and humbled heart God will not despise” (Ps.51:17).
Still, since the sorrow of one heart is generally concealed from another, and does not become obvious through words and similar signs – even when it is obvious to Him of whom it is said, “My groaning is not concealed from you” (Ps.38:9) – times of repentance have been rightly established by those placed over the churches, that satisfaction may also be made in the Church, in which the sins are forgiven. For, of course, outside her the sins are not forgiven. For she alone has received the pledge of the Holy Spirit (2 Cor.1:22) without whom there is no forgiveness of sins. Those forgiven thus obtain life everlasting.