The life of the Church is dependent on all its members

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

But a body calls also for a multiplicity of members, which are linked together in such a way as to help one another. And as in the body when one member suffers, all the other members share its pain, and the healthy members come to the assistance of the ailing, so in the Church the individual members do not live for themselves alone, but also help their fellows, and all work in mutual collaboration for the common comfort and for the more perfect building up of the whole Body.

Again, as in nature a body is not formed by any haphazard grouping of members but must be constituted of organs, that is of members, that have not the same function and are arranged in due order; so for this reason above all the Church is called a body, that it is constituted by the coalescence of structurally untied parts, and that it has a variety of members reciprocally dependent. It is thus the Apostle describes the Church when he writes: “As in one body we have many members, but all the members have not the same office: so we being many are one body in Christ, and everyone members one of another.”16

One must not think, however, that this ordered or “organic” structure of the body of the Church contains only hierarchical elements and with them is complete; or, as an opposite opinion holds, that it is composed only of those who enjoy charismatic gifts – though members gifted with miraculous powers will never be lacking in the Church. That those who exercise sacred power in this Body are its chief members must be maintained uncompromisingly. It is through them, by commission of the Divine Redeemer Himself, that Christ’s apostolate as Teacher, King and Priest is to endure. At the same time, when the Fathers of the Church sing the praises of this Mystical Body of Christ, with its ministries, its variety of ranks, its officers, it conditions, its orders, its duties, they are thinking not only of those who have received Holy Orders, but of all those too, who, following the evangelical counsels, pass their lives either actively among men, or hidden in the silence of the cloister, or who aim at combining the active and contemplative life according to their Institute; as also of those who, though living in the world, consecrate themselves wholeheartedly to spiritual or corporal works of mercy, and of those in the state of holy matrimony. Indeed, let this be clearly understood, especially in our days, fathers and mothers of families, those who are godparents through Baptism, and in particular those members of the laity who collaborate with the ecclesiastical hierarchy in spreading the Kingdom of the Divine Redeemer occupy an honorable, if often a lowly, place in the Christian community, and even they under the impulse of God and with His help, can reach the heights of supreme holiness, which, Jesus Christ has promised, will never be wanting to the Church.

16 Rom., XII, 4.

Mystici Corporis Christi 15-17

Scripture and the Magisterium attest that the Church is a visible body

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

If we would define and describe this true Church of Jesus Christ—which is the One, Holy, Catholic, Apostolic and Roman Church12—we shall find nothing more noble, more sublime, or more divine than the expression “the Mystical Body of Christ”—an expression which springs from and is, as it were, the fair flowering of the repeated teaching of the Sacred Scriptures and the Holy Fathers.

That the Church is a body is frequently asserted in the Sacred Scriptures. “Christ,” says the Apostle, “is the Head of the Body of the Church.”13 If the Church is a body, it must be an unbroken unity, according to those words of Paul: “Though many we are one body in Christ.”14 But it is not enough that the Body of the Church should be an unbroken unity; it must also be something definite and perceptible to the senses as Our predecessor of happy memory, Leo XIII, in his Encyclical Satis Cognitum asserts: “the Church is visible because she is a body.”15 Hence they err in a matter of divine truth, who imagine the Church to be invisible, intangible, a something merely “pneumatological” as they say, by which many Christian communities, though they differ from each other in their profession of faith, are untied by an invisible bond.

12 Cf. [First] Vat. Council, Const. de fide cath., c. 1.
13 Col., I, 18.
14 Rom., XII, 5.
15 Cf. Acta Sanctæ Sedis, XXVIII, p. 710.

Mystici Corporis Christi 13-14

The Mystical Body of Christ unites the faithful with Christ, their Head

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

After pondering all this long and seriously before God We consider it part of Our pastoral duty to explain to the entire flock of Christ through this Encyclical Letter the doctrine of the Mystical Body of Christ and of the union in this Body of the faithful with the divine Redeemer; and then, from this consoling doctrine, to draw certain lessons that will make a deeper study of this mystery bear yet richer fruits of perfection and holiness. Our purpose is to throw an added ray of glory on the supreme beauty of the Church; to bring out into fuller light the exalted supernatural nobility of the faithful who in the Body of Christ are united with their Head; and finally, to exclude definitely the many current errors with regard to this matter.

When one reflects on the origin of this doctrine, there come to mind at once the words of the Apostle: “Where sin abounded, grace did more abound.”6 All know that the father of the whole human race was constituted by God in so exalted a state that he was to hand on to his posterity, together with earthly existence, the heavenly life of divine grace. But after the unhappy fall of Adam, the whole human race, infected by the hereditary stain, lost their participation in the divine nature,7 and we were all “children of wrath.”8 But the all-merciful God “so loved the world as to give His only-begotten Son,”9 and the Word of the Eternal Father with the same divine love assumed human nature from the race of Adam – but as an innocent and spotless nature – so that He, as the new Adam, might be the source whence the grace of the Holy Spirit should flow unto all the children of the first parent. Through the sin of the first man they had been excluded from adoption as children of God; through the Word incarnate, made brothers according to the flesh of the only-begotten Son of God, they receive also the power to become the sons of God.10 As He hung upon the Cross, Christ Jesus not only appeased the justice of the Eternal Father which had been violated, but He also won for us, His brethren, an ineffable flow of graces. It was possible for Him of Himself to impart these graces to mankind directly; but He willed to do so only through a visible Church made up of men, so that through her all might cooperate with Him in dispensing the graces of Redemption. As the Word of God willed to make use of our nature, when in excruciating agony He would redeem mankind, so in the same way throughout the centuries He makes use of the Church that the work begun might endure.11

6 Rom., V, 20.
7 Cf. II Peter, I, 4.
8 Eph., II, 3.
9 John, III, 16.
10 Cf. John, I, 12.
11 Cf. [First] Vat. Council, Const. de Eccl., prol.

Mystici Corporis Christi 11-12

False rationalism and false mysticism both distort the Faith

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

For while there still survives a false rationalism, which ridicules anything that transcends and defies the power of human genius, and which is accompanied by a cognate error, the so-called popular naturalism, which sees and wills to see in the Church nothing but a juridical and social union, there is on the other hand a false mysticism creeping in, which, in its attempt to eliminate the immovable frontier that separates creatures from their Creator, falsifies the Sacred Scriptures.

As a result of these conflicting and mutually antagonistic schools of thought, some through vain fear, look upon so profound a doctrine as something dangerous, and so they shrink from it as from the beautiful but forbidden fruit of paradise. But this is not so. Mysteries revealed by God cannot be harmful to men, nor should they remain as treasures hidden in a field, useless. They have been given from on high precisely to help the spiritual progress of those who study them in a spirit of piety. For, as the [First] Vatican Council teaches, “reason illumined by faith, if it seeks earnestly, piously and wisely, does attain under God, to a certain and most helpful knowledge of mysteries, by considering their analogy with what it knows naturally, and their mutual relations, and their common relations with man’s last end,” although, as the same holy Synod observes, reason, even thus illumined, “is never capable of understanding those mysteries as it does those truths which forms its proper object.”5

5 Sessio III; Const. de fide cath., c. 4.

Mystici Corporis Christi 9-10

Increasing interest in the Faith and in liturgy brings cautious optimism

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

We have been no less consoled to know that with spontaneous generosity a fund has been created for the erection of a church in Rome to be dedicated to our saintly predecessor and patron, Eugene I. At this temple, to be built by the wish and through the liberality of all the faithful, will be a lasting memorial of this happy event, so We desire to offer this Encyclical Letter in testimony of Our gratitude. It tells of those living stones which rest upon the living cornerstone, which is Christ, and are built together into a holy temple, far surpassing any temple built by hands, into a habitation of God in the Spirit.4

But the chief reason for Our present exposition of this sublime doctrine is Our solicitude for the souls entrusted to Us. Much indeed has been written on this subject; and We know that many today are turning with greater zest to a study which delights and nourishes Christian piety. This, it would seem, is chiefly because a revived interest in the sacred liturgy, the more widely spread custom of frequent Communion, and the more fervent devotion to the Sacred Heart of Jesus practiced today, have brought many souls to a deeper consideration of the unsearchable riches of Christ which are preserved in the Church. Moreover, recent pronouncements on Catholic Action, by drawing closer the bonds of union between Christians and between them and the ecclesiastical hierarchy and especially the Roman Pontiff, have undoubtedly helped not a little to place this truth in its proper light. Nevertheless, while We can derive legitimate joy from these considerations, We must confess that grave errors with regard to this doctrine are being spread among those outside the true Church, and that among the faithful, also, inaccurate or thoroughly false ideas are being disseminated which turn minds aside from the straight path of truth.

4 Cf. Eph., II, 21-22; I Peter, II, 5.

Mystici Corporis Christi 7-8

The Mystical Body unites Catholics in charity under the protection of the Holy Father

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

Moreover, We trust that Our exposition of the doctrine of the Mystical Body of Christ will be acceptable and useful to those also who are without the fold of the Church, not only because their good will toward the Church seems to grow from day to day, but also because, while before their eyes nation rises up against nation, kingdom against kingdom, and discord is sown everywhere together with the seeds of envy and hatred, if they turn their gaze to the Church, if they contemplate her divinely-given unity—by which all men of every race are united to Christ in the bond of brotherhood—they will be forced to admire this fellowship in charity, and with the guidance and assistance of divine grace will long to share in the same union and charity.

There is a special reason too, and one most dear to Us, which recalls this doctrine to Our mind and with it a deep sense of joy. During the year that has passed since the twenty-fifth anniversary of Our Episcopal consecration, We have had the great consolation of witnessing something that has made the image of the Mystical Body of Jesus Christ stand out most clearly before the whole world. Though a long and deadly war has pitilessly broken the bond of brotherly union between nations, We have seen Our children in Christ, in whatever part of the world they happened to be, one in will and affection, lift up their hearts to the common Father, who, carrying in his own heart the cares and anxieties of all, is guiding the barque of the Catholic Church in the teeth of a raging tempest. This is a testimony to the wonderful union existing among Christians; but it also proves that, as Our paternal love embraces all peoples, whatever their nationality and race, so Catholics the world over, though their countries may have drawn the sword against each other, look to the Vicar of Jesus Christ as to the loving Father of them all, who, with absolute impartiality and incorruptible judgment, rising above the conflicting gales of human passions, takes upon himself with all his strength the defence of truth, justice and charity.

Mystici Corporis Christi 5-6

The present calamities of the Church and of souls resemble those of Christ

From Pope Pius XII’s encyclical Mystici Corporis Christi (1943):

From the outset it should be noted that the society established by the Redeemer of the human race resembles its divine Founder, who was persecuted, calumniated and tortured by those very men whom He had undertaken to save. We do not deny, rather from a heart filled with gratitude to God We admit, that even in our turbulent times there are many who, though outside the fold of Jesus Christ, look to the Church as the only haven of salvation; but We are also aware that the Church of God not only is despised and hated maliciously by those who shut their eyes to the light of Christian wisdom and miserably return to the teachings, customs and practices of ancient paganism, but is ignored and neglected, and even at times looked upon as irksome by many Christians who are allured by specious error or caught in the meshes of the world’s corruption. In obedience, therefore, Venerable Brethren, to the voice of Our conscience and in compliance with the wishes of many, We will set forth before the eyes of all and extol the beauty, the praises, and the glory of Mother Church to whom, after God, we owe everything.

And it is to be hoped that Our instructions and exhortations will bring forth abundant fruit in the souls of the faithful in the present circumstances. For We know that if all the sorrows and calamities of these stormy times, by which countless multitudes are being sorely tried, are accepted from God’s hands with calm submission, they naturally lift souls above the passing things of earth those of heaven that abide forever, and arouse a certain secret thirst and intense desire for spiritual things. Thus, urged by the Holy Spirit, men are moved, and as it were, impelled to seek the kingdom of God with greater diligence; for the more they are detached from the vanities of this world and from inordinate love of temporal things, the more apt they will be to perceive the light of heavenly mysteries. But the vanity and emptiness of earthly things are more manifest today than perhaps at any other period, when Kingdoms and States are crumbling, when enormous quantities of goods and all kinds of wealth are being sunk in the depths of the sea, and cities, towns and fertile fields are strewn with massive ruins and defiled with the blood of brothers.*

Mystici Corporis Christi 3-4

* Pope Pius issued this document during the Second World War.

Christ purchased the Church, His Mystical Body, with His Precious Blood

A traditional descriptor of the Church is that She is the Mystical Body of Christ, in which are united Our Lord as Head and the faithful as members. This unity is what we make reference to when we profess in the Creed that the Church is One and Catholic. It is also how we may distinguish true ecumenism (which seeks to resolve the causes of doctrinal division, most particularly between Catholicism and Orthodoxy) from false ecumenism (which seeks to minimize or dismiss the substantive doctrinal differences between Catholicism and non-Catholic creeds).

As the specters of false ecumenism and self-destruction loomed over Christendom and the world in the middle of the twentieth century, Pope Pius XII issued the encyclical Mystici Corporis Christi in 1943 to address the doctrine of the Mystical Body and its implications. We reproduce excerpts from that encyclical beginning today, and ask the intercession of Our Lady, Help of Christians, that the division and confusion now rampant in Christ’s Body and in the world may be healed.

The doctrine of the Mystical Body of Christ, which is the Church,1 was first taught us by the Redeemer Himself. Illustrating as it does the great and inestimable privilege of our intimate union with so exalted a Head, this doctrine by its sublime dignity invites all those who are drawn by the Holy Spirit to study it, and gives them, in the truths of which it proposes to the mind, a strong incentive to the performance of such good works as are conformable to its teaching. For this reason, We* deem it fitting to speak to you on this subject through this Encyclical Letter, developing and explaining above all, those points which concern the Church Militant. To this We are urged not only by the surpassing grandeur of the subject but also by the circumstances of the present time.

For We intend to speak of the riches stored up in this Church which Christ purchased with His own Blood,2 and whose members glory in a thorn-crowned Head. The fact that they thus glory is a striking proof that the greatest joy and exaltation are born only of suffering, and hence that we should rejoice if we partake of the sufferings of Christ, that when His glory shall be revealed we may also be glad with exceeding joy.3

1 Cf. Col. I, 24.
2 Acts, XX, 28.
3 Cf. I Peter, IV, 13.

Mystici Corporis Christi 1-2

* It is customary for a Pope to refer to himself in the first person plural, out of respect for the continuity and grave dignity of the Petrine office.