Missale Romanum: Promulgation of the New Missal by Paul VI

(From the Vatican website).
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The major innovation concerns the Eucharistic Prayer. If in the Roman Rite, the first part of this Prayer, the Preface, has preserved diverse formulation in the course of the centuries, the second part, on the contrary, called "Canon of the Action," took on an unchangeable form during the fourth and fifth centuries; conversely, the Eastern liturgies allowed for this variety in their anaphoras. In this matter, however, apart from the fact that the Eucharistic Prayer is enriched by a great number of Prefaces, either derived from the ancient tradition of the Roman Church or composed recently, we have decided to add three new Canons to this Prayer. In this way the different aspects of the mystery of salvation will be emphasized and they will procure richer themes for the thanksgiving. However, for pastoral reasons, and in order to facilitate concelebration, we have ordered that the words of the Lord ought to be identical in each formulary of the Canon. Thus, in each Eucharistic Prayer, we wish that the words be pronounced thus: over the bread: ACCIPITE ET MANDUCATE EX HOC OMNES: HOC EST ENIM CORPUS MEUM, QUOD PRO VOBIS TRADETUR; over the chalice: ACCIPITE ET BIBITE EX EO OMNES: HIC EST ENIM CALIX SANGUINIS MEI NOVI ET AETERNI TESTAMENTI, QUI PRO VOBIS ET PRO MULTIS EFFUNDETUR IN REMISSIONEM PECCATORUM. HOC FACITE IN MEAM COMMEMORATIONEM. The words MYSTERIUM FIDEI, taken from the context of the words of Christ the Lord, and said by the priest, serve as an introduction to the acclamation of the faithful.
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In conclusion, we wish to give the force of law to all that we have set forth concerning the new Roman Missal. In promulgating the official edition of the Roman Missal, Our predecessor, St. Pius V, presented it as an instrument of liturgical unity and as a witness to the purity of the worship the Church. While leaving room in the new Missal, according to the order of the Second Vatican Council, "for legitimate variations and adaptations,"(15) we hope nevertheless that the Missal will be received by the faithful as an instrument which bears witness to and which affirms the common unity of all. Thus, in the great diversity of languages, one unique prayer will rise as an acceptable offering to our Father in heaven, through our High-Priest Jesus Christ, in the Holy Spirit.

We order that the prescriptions of this Constitution go into effect November 30th of this year, the first Sunday of Advent.

We wish that these Our decrees and prescriptions may be firm and effective now and in the future, notwithstanding, to the extent necessary, the apostolic constitutions and ordinances issued by Our predecessors, and other prescriptions, even those deserving particular mention and derogation.