Mystici corporis Christi

The encyclical teaches that both lay people and the leadership have a role to play in the Church. Lay people are at the forefront of the Church, and have to be aware of 'being the Church', not just 'belonging to the Church'. At the same time, the Pope and bishops are responsible for providing leadership for all the faithful. Together, they are the Church and work for the good of the Church.[10]

In 1947, Pius XII later issued the Apostolic Constitution Provida Mater Ecclesia, which allowed lay people to form their own secular communities, and establish them within a newly established Canon Law framework.[11]

The encyclical states that Christ, while still on earth, instructed by precept, counsel and warnings "in words that shall never pass away, and will be spirit and life"[12] to all men of all times. He conferred a triple power on His Apostles and their successors, to teach, to govern, to lead men to holiness, making this power, defined by special ordinances, rights and obligations, the fundamental law of the whole Church.[13] God governs directly and guides personally the Church which He founded. Pius XII quoted Proverbs 21:1 noting that God reigns within the minds and hearts of men, and bends and subjects their wills to His good pleasure, even when rebellious.[14]

Mystici corporis requests the faithful to love their Church and to always see Christ in her, especially in the old and sick members. They must accustom themselves to see Christ Himself in the Church. For it is Christ who lives in His Church, and through her, teaches, governs, and sanctifies; it is Christ also who manifests Himself differently in different members of His society.

If the faithful strive to live in a spirit of lively faith, they will not only pay due honor and reverence "to the more exalted members" of this Mystical Body, especially those who according to Christ's mandate will have to render an account of our souls, but they will take to their hearts those members who are the object of our Savior's special love: the weak, the wounded, and the sick who are in need of material or spiritual assistance; children whose innocence is so easily exposed to danger in these days; and finally the poor, in helping whom is recognized the very person of Jesus Himself as a perfect model of love for the Church.[15]

Pius XII wrote: "The Church of God … 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." He quoted the book of Wisdom to the effect that "a most severe judgment shall be for them that bear rule. ...The mighty shall be mightily tormented. ...A greater punishment is ready for the more mighty."[16] Ronald Rychlak has described the encyclical as "an obvious attack on the theoretical basis of National Socialism."[17]

Pius' statement of "profound grief" at the murder of the deformed, the insane, and those suffering from hereditary disease... as though they were a useless burden to Society" was a condemnation of the ongoing Nazi euthanasia program, under which disabled Germans were being removed from care facilities and murdered by the state as "life unworthy of life". It built upon the high-profile condemnations offered by the bishop of Munster, Clemens August Graf von Galen and others. It was followed, on 26 September 1943, by an open condemnation by the German Bishops which, from every German pulpit, denounced the killing of "innocent and defenceless mentally handicapped, incurably infirm and fatally wounded, innocent hostages, and disarmed prisoners of war and criminal offenders, people of a foreign race or descent".[18]

Pius XII appealed to "Catholics the world over" to "look to the Vicar of Jesus Christ as the loving Father of them all, who… takes upon himself with all his strength the defense of truth, justice and charity." He explained, "Our paternal love embraces all peoples, whatever their nationality or race." Christ, by his blood, made the Jews and Gentiles one "breaking down the middle wall of partition… in his flesh by which the two peoples were divided." He noted that Jews were among the first people to adore Jesus. Pius then made an appeal for all to "follow our peaceful King who taught us to love not only those who are of a different nation or race, but even our enemies." Pinchas E. Lapide, the Israeli consul in Italy, wrote: "Pius chose mystical theology as a cloak for a message which no cleric or educated Christian could possibly misunderstand."[16]

In the United States, it would be seen as a critique of any kind of prejudice against African-Americans.[19]

Mystici corporis Christi strongly condemned the forced conversions to Catholicism that were then occurring in Fascist Croatia.[20] Church membership and conversions must be voluntary. Regarding conversions, "We recognize that this must be done of their own free will; for no one believes unless he wills to believe."[21] Hence they are most certainly not genuine Christians who against their belief are forced to go into a church, to approach the altar and to[22] receive the Sacraments; for the "faith without which it is impossible to please God" is an entirely free "submission of intellect and will."[23]

The encyclical concludes with a summary of the mariology of the Pope. The 1854 dogma of the Immaculate Conception by Pius IX defined the Virgin conceived without sin, as the mother of God and our mother. Pope Pius XII built on this in Mystici corporis: Mary, whose sinless soul was filled with the divine spirit of Jesus Christ above all other created souls, "in the name of the whole human race" gave her consent "for a spiritual marriage between the Son of God and human nature",[24] thus elevating human nature beyond the realm of the purely material. She who, according to the flesh, was the mother of our Head, became mother of all His members. Through her powerful prayers, she obtained that the spirit of our Divine Redeemer, should be bestowed on the newly founded Church at Pentecost.[25]

While the Early Fathers of the Church tended to contrast Eve's disobedience with Mary's fiat at the Annunciation, Pius looked rather to her presence at Calvary where "...she, the second Eve, who, free from all sin, original or personal, and always more intimately united with her Son, offered Him on Golgotha to the Eternal Father for all the children of Adam, sin-stained by his unhappy fall."[26] Pius viewed her compassion there as the basis for her role in redemption.[27]

If the Mother of God was born as the "second Eve", the Church was born as the "new Eve". Pius XII repeated that, according to "unanimous teaching" of the holy Fathers and the magisterium of Christ, the "Church was born from the side of our Savior on the Cross like a new Eve, mother of all the living."[26]

The encyclical is principally remembered for its statement that the Mystical Body is identical with the Roman Catholic Church, repeated by Pius XII in Humani generis (1950) in response to dissension. According to Mystici corporis, to be truly (reapse) a member of the Mystical Body one must be a member of the Roman Catholic Church. Other Christians who erred in good faith could be unsuspectingly united to the Mystical Body by an unconscious desire and longing (inscio quodam desiderio ac voto). In 1947, Pius XII wrote the encyclical Mediator Dei which acknowledged that baptized Christians were members of the Mystical Body and participated in Christ's priestly office.[2]

During the Second Vatican Council, Yves Congar argued that the term ecclesia ('church') concerned the people "called forth", the People of God, those over whom God reigns. "Body of Christ" then would emphasize the special union with the risen Christ that came with the new covenant. Congar was later denounced by the Holy Office for describing the Church as essentially a community in the Spirit, a gathering of the faithful.[2]

The Second Vatican Council would later define in Lumen gentium that the Church subsists in (subsistit in) the Catholic Church. Dulles argues this to be "an expression deliberately chosen to allow for the ecclesial reality of other Christian communities", implying that non-Catholic Christians are members of the Body of Christ, and thus of the Church.[2]