From Dom Guéranger's The Liturgical Year.
The solemnity of Pentecost and its octave are over, and the progress of the liturgical year introduces us into a new period, which is altogether different from those we have hitherto spent. From the very beginning of Advent, which is the prelude to the Christmas festival, right up to the anniversary of the descent of the Holy Ghost, we have witnessed the entire series of the mysteries of our redemption; all have been unfolded to us. The sequel of seasons and feasts made up a sublime drama, which absorbed our very existence; we have but just come from the final celebration, which was the consummation of the whole. And yet we have gone through but one half of the year. This does not imply that the period we have still to live is devoid of its own special mysteries; but, instead of keeping up our attention by the ceaseless interest of one plan hurrying on to its completion, the sacred liturgy is about to put before us an almost unbroken succession of varied episodes, of which some are brilliant with glory, and others exquisite in loveliness, but each one of them bringing its special tribute towards either the development of the dogmas of faith or the furtherance of the Christian life. This year’s cycle will thus be filled up; it will disappear; a new one will take its place, bringing before us the same divine facts, and pouring forth the same graces on Christ’s mystical body.
This section of the liturgical year, which comprises a little more or a little less than six months according as Easter is early or late, has always had the character it holds at present. But, although it admits only detached solemnities and feasts, the influence of the movable portion of the cycle is still observable. It may have as many as twenty-eight or as few as twenty-three weeks. This variation depends not only upon the Easter feast, which may occur on any of the days between March 22 and April 25 inclusively, but also on the date of the first Sunday of Advent, which is the opening of a new ecclesiastical year, and is always the Sunday nearest the Kalends of December.
In the Roman liturgy the Sundays of this series go under the name of ‘Sundays after Pentecost.’ As we shall show in the next chapter, that title is the most suitable that could have been given, and is found in the oldest sacramentaries and antiphonaries, but it was not universally adopted even by those Churches which followed the Roman rite; in progress of time, however, that title became the general one. To mention some of the previous early names: in the Comes of Alcuin, which takes us back to the eighth century, we find the first section of these Sundays called ‘Sundays after Pentecost’; the second is named ‘weeks after the feast of the Apostles’ (post natale Apostolorum); the third goes under the title of ‘weeks after St. Laurence’ (post Sancti Laurentii); the fourth has the appellation of ‘weeks of the seventh month’ (September); and, lastly, the fifth is termed ‘weeks after St. Michael’ (post Sancti Angeli), and lasts till Advent. As late as the sixteenth century many missals of the western Churches gave us these several sections of the Time after Pentecost, but some of the titles varied according to the special saints honoured in the respective dioceses, whose feasts were taken as the date-marks of this period of the year. The Roman missal, published by order of St. Pius V, has gradually been adopted in all our Latin churches, and has restored the ancient denomination to the ecclesiastical season we have just entered upon; so that the only name under which it is now known amongst us is ‘the Time after Pentecost’ (post Pentecosten).