Today is the Solemnity of Christ the King of the Universe in the Ordinary Form; it is also the last Sunday of Ordinary Time--Advent begins next Sunday. In the Extraordinary Form we celebrated the Solemnity of Christ the King on the last Sunday of October, before the Solemnity of All Saints. The New Liturgical Movement site posted a link to an explanation of the different purposes of the different timings of this great solemnity--as originally intended by Pope Pius XI in 1925 and as intended after the Second Vatican Council:
Pius XI’s intention, as can be gleaned from n. 29 [of the , is to emphasize the glory of Christ as terminus of His earthly mission,a glory and mission visible and perpetuated in history by the saints. Hence the feast falls shortly before the Feast of All Saints, to emphasize that what Christ inaugurated in His own person before ascending in glory, the saints then instantiate and carry further in human society, culture, and nations. It is a feast primarily about celebrating Christ’s ongoing kingship over all reality, including this present world, where the Church must fight for the recognition of His rights, the actual extension of His dominion to all domains, individual and social.
Indeed, there's also the obvious fact, unmentioned in Quas Primas but surely in everyone's mind, that the last Sunday in October had, for centuries, been celebrated as Reformation Sunday. A Catholic counter-feast, reminding the world not only of the comprehensive Kingship of Jesus Christ—so often denied socially and culturally by various teachings of Protestantism—but also of the worldwide kingly authority of His Church, would certainly be a reasonable application of the principle lex orandi, lex credendi.
In the liturgical reforms following the Second Vatican Council, its place was changed to the last Sunday of the Church year—that is, so that one week later would fall the first Sunday of Advent. This new position emphasizes rather the eschatological dimension of Christ’s kingship: the Kingdom of Jesus Christ, though begun in time, is here present “as in a mystery” (as Lumen Gentium phrases it) and in a “crucified” way. This Kingdom will be perfected and fully manifested only at the end of time, with the Second Coming. Hence in the new calendar the feast comes at the very end of the Church’s year, as the summation of the whole of salvation history and the symbol of what we hope for:expectantes … adventum salvatoris nostri Jesu Christi, as the liturgy in the Ordinary Form proclaims after the Lord’s Prayer.
Read the rest here.