Mysterii Paschalis

Mysterii Paschalis is the incipit of an apostolic letter issued motu proprio (that is, "of his own accord") by Pope Paul VI on 14 February 1969. It reorganized the liturgical year of the Roman Rite and revised the liturgical celebrations of Jesus Christ and the saints in the General Roman Calendar.

First Sentence: Mysterii Paschalis celebrationem potissimum habere in religioso christianorum cultu momentum, eandemque per dierum, hebdomadarum totiusque anni explicari cursum, dilucide sacrosancto Concilio Vaticano II docemur. Ex quo sequitur, opus esse, ut idem paschale Christi mysterium in instauratione anni liturgici, cuius normae ab ipsa Sancta Synodo tradita sunt, in clariore luce ponatur, sive ad ordinationem Proprii, quod vocant, de Tempore ac de Sanctis, sive ad Calendarii Romani recognitionem quod attinet.

By this document, Pope Paul VI implemented the Second Vatican Council's norms for restoring the liturgical year and "approve[d] by Our apostolic authority…the new Roman Universal Calendar…and likewise the general norms concerning the arrangement of the liturgical year".

On 21 March of the same year the Congregation of Rites promulgated the revised norms on the liturgical year and the calendar by a decree signed by the Prefect Cardinal Benno Gut and the Secretary Ferdinando Giuseppe Antonelli. The motu proprio and the decree were included, with an unofficial commentary by the Council for the Proper Implementation of the Constitution on the Sacred Liturgy, in the book Calendarium Romanum (Libreria Editrice Vaticana, 1969).

The new norms became effective on 1 January 1970.

...
Wikipedia