...Some are more easily deceived by the outward appearance of good when there is question of fostering unity among all Christians.
4. Is it not right, it is often repeated, indeed, even consonant with duty, that all who invoke the name of Christ should abstain from mutual reproaches and at long last be united in mutual charity? Who would dare to say that he loved Christ, unless he worked with all his might to carry out the desires of Him, Who asked His Father that His disciples might be “one.”[1] And did not the same Christ will that His disciples should be marked out and distinguished from others by this characteristic, namely that they loved one another: “By this shall all men know that you are my disciples, if you have love one for another”?[2] All Christians, they add, should be as “one”: for then they would be much more powerful in driving out the pest of irreligion, which like a serpent daily creeps further and becomes more widely spread, and prepares to rob the Gospel of its strength. These things and others that class of men who are known as pan-Christians continually repeat and amplify; and these men, so far from being quite few and scattered, have increased to the dimensions of an entire class, and have grouped themselves into widely spread societies, most of which are directed by non-Catholics, although they are imbued with varying doctrines concerning the things of faith. This undertaking is so actively promoted as in many places to win for itself the adhesion of a number of citizens, and it even takes possession of the minds of very many Catholics and allures them with the hope of bringing about such a union as would be agreeable to the desires of Holy Mother Church, who has indeed nothing more at heart than to recall her erring sons and to lead them back to her bosom. But in reality beneath these enticing words and blandishments lies hid a most grave error, by which the foundations of the Catholic faith are completely destroyed.
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10. So, Venerable Brethren, it is clear why this Apostolic See has never allowed its subjects to take part in the assemblies of non-Catholics: for the union of Christians can only be promoted by promoting the return to the one true Church of Christ of those who are separated from it, for in the past they have unhappily left it. To the one true Church of Christ, we say, which is visible to all, and which is to remain, according to the will of its Author, exactly the same as He instituted it. During the lapse of centuries, the mystical Spouse of Christ has never been contaminated, nor can she ever in the future be contaminated, as Cyprian bears witness: “The Bride of Christ cannot be made false to her Spouse: she is incorrupt and modest. She knows but one dwelling, she guards the sanctity of the nuptial chamber chastely and modestly.”[20] The same holy Martyr with good reason marveled exceedingly that anyone could believe that “this unity in the Church which arises from a divine foundation, and which is knit together by heavenly sacraments, could be rent and torn asunder by the force of contrary wills.”[21] For since the mystical body of Christ, in the same manner as His physical body, is one,[22] compacted and fitly joined together,[23] it were foolish and out of place to say that the mystical body is made up of members which are disunited and scattered abroad: whosoever therefore is not united with the body is no member of it, neither is he in communion with Christ its head.[24]
11. Furthermore, in this one Church of Christ no man can be or remain who does not accept, recognize and obey the authority and supremacy of Peter and his legitimate successors. Did not the ancestors of those who are now entangled in the errors of Photius and the reformers, obey the Bishop of Rome, the chief shepherd of souls? Alas their children left the home of their fathers, but it did not fall to the ground and perish for ever, for it was supported by God. Let them therefore return to their common Father, who, forgetting the insults previously heaped on the Apostolic See, will receive them in the most loving fashion. For if, as they continually state, they long to be united with Us and ours, why do they not hasten to enter the Church, “the Mother and mistress of all Christ’s faithful”?[25] Let them hear Lactantius crying out: “The Catholic Church is alone in keeping the true worship. This is the fount of truth, this the house of Faith, this the temple of God: if any man enter not here, or if any man go forth from it, he is a stranger to the hope of life and salvation. Let none delude himself with obstinate wrangling. For life and salvation are here concerned, which will be lost and entirely destroyed, unless their interests are carefully and assiduously kept in mind.”[26]
12. Let, therefore, the separated children draw nigh to the Apostolic See, set up in the City which Peter and Paul, the Princes of the Apostles, consecrated by their blood; to that See, We repeat, which is “the root and womb whence the Church of God springs,”[27] not with the intention and the hope that “the Church of the living God, the pillar and ground of the truth”[28] will cast aside the integrity of the faith and tolerate their errors, but, on the contrary, that they themselves submit to its teaching and government. Would that it were Our happy lot to do that which so many of Our predecessors could not, to embrace with fatherly affection those children, whose unhappy separation from Us We now bewail. Would that God our Savior, “Who will have all men to be saved and to come to the knowledge of the truth,”[29] would hear us when We humbly beg that He would deign to recall all who stray to the unity of the Church! In this most important undertaking We ask and wish that others should ask the prayers of Blessed Mary the Virgin, Mother of divine grace, victorious over all heresies and Help of Christians, that She may implore for Us the speedy coming of the much hoped-for day, when all men shall hear the voice of Her divine Son, and shall be “careful to keep the unity of the Spirit in the bond of peace.”[30]