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The Church is one, which is spread abroad far and wide into a multitude by an increase of fruitfulness, as there are many rays of the sun, but one light; and many branches of a tree, but one strength based in its tenacious root; and since from one spring flow many streams, although the multiplicity seems diffused in the liberality of an overflowing abundance, yet the unity is still preserved in the source. Try to separate a ray of the sun from its body of light, its unity does not allow a division of light. Break a branch from a tree -- when broken, it will not be able to bud; cut off the stream from its fountain, and that which is cut off dries up. Thus also the Church, shone over with the light of the Lord, sheds forth her rays over the whole world, yet it is one light which is everywhere diffused, nor is the unity of the body separated. Her fruitful abundance spreads her branches over the whole world. She broadly expands her rivers, liberally flowing, yet her head is one, her source one; and she is one Mother, plentiful in the results of fruitfulness: from her womb we are born, by her milk we are nourished, by her spirit we are animated.
The Bride of Christ cannot be adulterous; she is uncorrupted and pure. She knows one home; she guards with chaste modesty the sanctity of one couch. She keeps us for God. She appoints the sons whom she has born for the Kingdom. Whoever is separated from the Church and is joined to an adulteress, is separated from the promises of the Church; nor can he who forsakes the Church of Christ attain to the rewards of Christ. He is a stranger; he is profane; he is an enemy. He can no longer have God for his Father, who has not the Church for his Mother. If any one could escape who was outside the ark of Noah, then he also may escape who shall be outside of the Church. The Lord warns, saying, ‘He who is not with Me is against Me, and he who gathers not with Me scatters’ (Mt 12, 30). He who breaks the peace and the harmony of Christ does so in opposition to Christ; he who gathers elsewhere than in the Church, scatters the Church of Christ. The Lord says, ‘I and the Father are One’ (Io 10, 30); and again it is written of the Father, and of the Son, and of the Holy Spirit, ‘And these Three are One” (1 Io 5, 7). And does any one believe that this unity which thus comes from the divine strength and is united in heavenly sacraments, can be divided in the Church, and can be separated by the parting asunder of opposing wills? He who does not hold this unity does not hold God’s law, does not hold the faith of the Father and the Son, and is separated from life and salvation.
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God is One, and Christ is One, and His Church is One, and the faith is One, and the people are joined into a substantial unity of body by the cement of harmony. Unity cannot be severed; nor can one body be separated by a division of its structure, nor torn into pieces, nor have its limbs torn. Whatever has proceeded from the womb cannot live and breathe in its detached condition, but loses the substance of health. The Holy Spirit warns us, and says, ‘What man is he that desires to live, and longs for good days? Refrain your tongue from evil, and your lips that they speak no guile. Eschew evil, and do good; seek peace, and ensue it’ (Ps 33, 12). The son of peace ought to seek peace and ensue it. He who knows and loves the bond of charity, ought to refrain his tongue from the evil of dissension. Among His divine commands and salutary teachings, the Lord, when He was now very near to His Passion, added this one, saying, ‘Peace I leave with you, My peace I give unto you’ (Io 14, 27). He gave this to us as a heritage; He promised all the gifts and rewards of which He spoke through the preservation of peace. If we are fellow-heirs with Christ, let us abide in the peace of Christ; if we are sons of God, we ought to be peacemakers. ‘Blessed’, says He, ‘are the peacemakers; for they shall be called the sons of God’ (Mt 5, 9). It benefits the sons of God to be peacemakers, gentle in heart, simple in speech, agreeing in affection, faithfully linked to one another in the bonds of unanimity.