MEDIATOR DEI. - The words with which the encyclical of Pius XII, dated 20 Nov. 1947 (AAS, 39 [1947], pp. 521-95), on the sacred liturgy begins. It may be considered a complement to the encyclical Mystici corporis (v.), since the Supreme Pontiff responds to the further demands (pointed out by Msgr. Gröber as early as 1943, v. bibl.) of the modern liturgical movement, intimately connected with the revival of ecclesiological studies. The response is given indirectly, with careful asides, conceived as parts of the broad doctrinal development, which is conducted with tight logic and supported by wide and clear information.
The encyclical opens with the concept of the liturgy as the public worship of the Church, whose origin and homogeneous development, constantly directed by the hierarchical authority, it describes (part 1); it then considers the holy Mass as the center of the liturgy, illustrating its essence (sacramental immolation), the participation of the faithful, and its integration into the Eucharistic banquet and the worship of adoration (part 2); it next studies the prolongation of the Eucharistic worship in the laus perennis of the Divine Office, explaining its intimate meaning in the light of the concentric cycles of Christ, of the Virgin, and of the saints (part 3). This substantial document closes with an exhortation on individual piety (the complement of public worship) and on the liturgical spirit and apostolate (part 4).
The great encyclical (it is the most extensive of all those issued so far) is studded with weighty dogmatico-liturgical affirmations, for example, on the nature of the liturgy, on the essence of the Mass, on the participation of the faithful in the Eucharistic Sacrifice, on the harmony of the opus operatum (objective piety) and the opus operantis (subjective piety), on individual piety, on the essential distinction between the hierarchical priesthood of priests and the mystical priesthood of the faithful (regale sacerdotium), on the unfounded distinction between the historical Christ and the pneumatic Christ, on the exaggerations of certain liturgical centers, on the progressive development of liturgical forms, on the relations between the Cross and the Altar, on the presence of Jesus Christ in the righteous soul.
A direct response to the memorandum of Msgr. Gröber, the encyclical is a solemn taking of a position by the Apostolic See in the now centuries-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: the one and the other form two conspicuous panels of a single diptych.
Bibliography12 works
604; A. Michel, Sur la présence de l'humanité du Christ glorieux dans les justifiés, in L'ami du clergé, 60 (1950), pp. 91-93; B. Cappelle, Autour de l'encycl. M. D., in Les questions liturgiques et paroissiales, 31 (1950), pp. 12-17 (esame critico dei commenti alla M. D.); id., La Communion pendant la Messe d'après l'encycl. M. D., ibid., 31 (1950), pp. 166-70; vari autori, Commento alla M. D., in Revista Ecclesiastica Brasileira, 11 (1951), pp. 1-224 (tutto consacrato all'argomento).