Mystici Corporis Christi (The Mystical Body of Christ) is an encyclical issued by Pope Pius XII on 29 June 1943 during World War II.

[1] According to the Jesuit theologian Avery Dulles, Mystici Corporis was "the most comprehensive official Catholic pronouncement on the Church prior to Vatican II".

[1] The encyclical builds on a theological development in the 1920s and 1930s in Italy, France, Germany and England, which all re-discovered the Pauline concept of the Mystical Body of Christ.

[6] 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" to all men of all times.

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.

[10] 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".

[14] 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".

Pius then made an appeal for all to "follow our peaceful King [Jesus Christ] who taught us to love not only those who are of a different nation or race, but even our enemies".

[16] It states that the only ones who can be considered as "members of the Church" are those "who have been baptized and profess the true faith, and who have not […] separate[d] themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed".

It was through her powerful prayers obtained that the spirit of our Divine Redeemer, already given on the Cross, should be bestowed, accompanied by miraculous gifts, on the newly founded Church at Pentecost; and finally, bearing with courage and confidence the tremendous burden of her sorrows and desolation, she, truly the Queen of Martyrs".

[14] Mystici Corporis Christi is principally remembered for its statement that the Mystical Body of Christ is identical with the Roman Catholic Church, a position later reaffirmed by Pius XII in Humani generis (1950) in response to dissension.

[a][1] 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.

Paul VI's 1964 encyclical letter Ecclesiam Suam quotes Mystici Corporis Christi:Consider, then, this splendid utterance of Our predecessor: "The doctrine of the Mystical Body of Christ, which is the Church, a doctrine revealed originally from the lips of the Redeemer Himself, and making manifest the inestimable boon of our most intimate union with so august a Head, has a surpassing splendor which commends it to the meditation of all who are moved by the divine Spirit, and with the light which it sheds on their minds, is a powerful stimulus to the salutary conduct which it enjoins.