9 The Eucharist, as Christ's saving presence in the community of the faithful and its spiritual food, is the most precious possession which the Church can have in her journey through history. This explains the lively concern which she has always shown for the Eucharistic mystery, a concern which finds authoritative expression in the work of the Councils and the Popes. How can we not admire the doctrinal expositions of the Decrees on the Most Holy Eucharist and on the Holy Sacrifice of the Mass promulgated by the Council of Trent? For centuries those Decrees guided theology and catechesis, and they are still a dogmatic reference-point for the continual renewal and growth of God's People in faith and in love for the Eucharist. In times closer to our own, three Encyclical Letters should be mentioned: the Encyclical Mirae Caritatis of Leo XIII (28 May 1902), the Encyclical Mediator Dei of Pius XII (20 November 1947) and the Encyclical Mysterium Fidei of Paul VI (3 September 1965). The Second Vatican Council, while not issuing a specific document on the Eucharistic mystery, considered its various aspects throughout its documents, especially the Dogmatic Constitution on the Church Lumen Gentium and the Constitution on the Sacred Liturgy Sacrosanctum Concilium . I myself, in the first years of my apostolic ministry in the Chair of Peter, wrote the Apostolic Letter Dominicae Cenae (24 February 1980), in which I discussed some aspects of the Eucharistic mystery and its importance for the life of those who are its ministers. Today I take up anew the thread of that argument, with even greater emotion and gratitude in my heart, echoing as it were the word of the Psalmist: “What shall I render to the Lord for all his bounty to me? I will lift up the cup of salvation and call on the name of the Lord” ( Ps 116:12-13).
Source: Ecclesia de Eucharistia (Vatican.va)