« MEDIATOR DEI ». - Words with which begins the encyclical of Pius XII, issued on 20 Nov. 1947 (AAS, 39 [1947], pp. 521-95), on the sacred liturgy. It may be considered a Mystici Corporis (v.), since the Supreme Pontiff responds to further demands (signaled by Abp. Gröber as early as 1943, V. BIBLICA.) of the modern liturgical movement, which is intimately connected with the revival of ecclesiastical studies. The response is given indirectly, through careful asides, conceived as parts of the broad doctrinal development, which is conducted with rigorous logic and supported by extensive and clear information.
The encyclical begins with the concept of liturgy as the public worship of the Church, describing its origin and homogeneous development, constantly directed by hierarchical authority (Part 1); it then considers the Holy Mass as the center of the liturgy, illustrating its essence (sacramental immolation), the participation of the faithful, its integration into the Eucharistic banquet and the cult of adoration (Part 2); it subsequently studies the extension of Eucharistic worship in the laus perennis of the Divine Office, explaining its intimate meaning in the light of the concentric cycles of Christ, the Virgin, and the saints (Part 3). The substantial document closes with an exhortation on individual piety (complementary to public worship) and on the spirit and apostolate of the liturgy (Part 4).
This great encyclical (the longest of all those issued to date) is studded with weighty dogmatic-liturgical affirmations, e.g., on the nature of the liturgy, the essence of the Mass, the participation of the faithful in the Eucharistic Sacrifice, the harmony between the opus operatum (objective piety) and the opus operantis (subjective piety), individual piety, the essential distinction between the hierarchical priesthood of priests and the priesthood of the faithful (regale sacerdotium), the unfounded distinction between the historical Christ and the pneumatic Christ, the exaggerations of certain liturgical centers, the progressive development of liturgical forms, the relationship between the Cross and the Altar, and the presence of Jesus Christ in the just soul.
A direct response to the memorandum of Abp. Gröber, the encyclical is a solemn position-taking by the Apostolic See in the now-century-old liturgical movement, whose beneficial course it does not halt but whose deviations it corrects and whose tendencies it disciplines. It is a continuation of the pontifical teaching begun with the encyclical Mystici Corporis: both form two striking panels of the same diptych.