On the Thursday nine weeks after Holy Thursday falls the feast of Corpus Christi — specifically, the Body of Christ, not the Novus Ordo’s substitute commemoration “the Body and Blood of Christ,” which is in any case usually transferred to Sunday (and is not by any means the same as an “external solemnity”) on account of the hierarchy’s nearly-unanimous surrender to the imperious dictatorship of work. (The traditional calendar, thanks to Pius IX, appropriately includes a feast for the Most Precious Blood of Jesus on July 1st, a theme to which John XXIII dedicated an encyclical in 1960.) Like the Ascension, Corpus Christi falls properly on a Thursday: always has, always will, wherever tradition is valued as befits Catholics.
Corpus Christi was originally instituted as an octave. Whoever believes that Our Lord is really, truly, substantially present in the Most Holy Sacrament would not be able to celebrate this “incomprehensible mystery of love” for just one day and then move on, like a person checking off a task on his to-do list and moving on to the next. No, there must be the full, rounded, lavish praise of eight days: time stands still and we bask in the glory of the Incarnate God in our midst until the end of time and the end of signs.
So obvious is this ecclesial instinct that when Our Lord Himself appeared to St. Margaret Mary Alacoque to ask for the institution of a feast in honor of His Sacred Heart, He specified that it was to take place on “the Friday after the octave of Corpus Christi” (see here for further details). That is why it occurs the Friday of the week following the feast. It has retained this spot in the 1962 and 1969 calendars, a position that would seem rather random in the absence of the octave; it’s like the “ghost pain” where a severed limb used to be, which Descartes used as evidence of the untrustworthiness of the senses. My view is that if the octave’s good with Jesus, it’s good with me.
Although the abolition of this octave was one of many egregious preconciliar liturgical deformations that happened under Pius XII, mid-way between the gutting of the Psalter (1911) and the gutting of the entire Roman rite (1969 and environs), today we may rejoice that, thanks to discreet indications from the quondam Pontifical Commission Ecclesia Dei, the octave of Corpus Christi may be observed today, in this happy period of the restoration of the Tridentine rite. The 2020 Ordo for the Usus Antiquior, published by the Congregation for the Doctrine of the Faith, indicates that the Octave of Corpus Christi may be observed in some fashion. (Incidentally, it also says that the Preface of the Nativity may be used.) It doesn’t explain how it is it to be observed, but probably assumes that anyone who is competent to read these rubrics in Latin can figure out from an old missal what to do. Here is a photo of the page from the 2021 Ordo:
Corpus Christi was originally instituted as an octave. Whoever believes that Our Lord is really, truly, substantially present in the Most Holy Sacrament would not be able to celebrate this “incomprehensible mystery of love” for just one day and then move on, like a person checking off a task on his to-do list and moving on to the next. No, there must be the full, rounded, lavish praise of eight days: time stands still and we bask in the glory of the Incarnate God in our midst until the end of time and the end of signs.
So obvious is this ecclesial instinct that when Our Lord Himself appeared to St. Margaret Mary Alacoque to ask for the institution of a feast in honor of His Sacred Heart, He specified that it was to take place on “the Friday after the octave of Corpus Christi” (see here for further details). That is why it occurs the Friday of the week following the feast. It has retained this spot in the 1962 and 1969 calendars, a position that would seem rather random in the absence of the octave; it’s like the “ghost pain” where a severed limb used to be, which Descartes used as evidence of the untrustworthiness of the senses. My view is that if the octave’s good with Jesus, it’s good with me.
Although the abolition of this octave was one of many egregious preconciliar liturgical deformations that happened under Pius XII, mid-way between the gutting of the Psalter (1911) and the gutting of the entire Roman rite (1969 and environs), today we may rejoice that, thanks to discreet indications from the quondam Pontifical Commission Ecclesia Dei, the octave of Corpus Christi may be observed today, in this happy period of the restoration of the Tridentine rite. The 2020 Ordo for the Usus Antiquior, published by the Congregation for the Doctrine of the Faith, indicates that the Octave of Corpus Christi may be observed in some fashion. (Incidentally, it also says that the Preface of the Nativity may be used.) It doesn’t explain how it is it to be observed, but probably assumes that anyone who is competent to read these rubrics in Latin can figure out from an old missal what to do. Here is a photo of the page from the 2021 Ordo:
As I’ve mentioned on other occasions, Anglophone traditionalists are sometimes too legalistic when it comes to asking and waiting for explicit “permissions” from “the Vatican” to do X, Y, or Z. The way things are done in Rome is very Italian: hints are dropped, nudges are given, a quiet wave of the hand. Often, the lack of a prohibition or an outcry in view of obviously known cases can be construed as “soft” approval to continue. This is very important for restoring the fullness of the Roman Rite of the Mass (especially its calendar), which suffered intensifying depradations of bad taste and bad theology from the 1940s onward, beginning with the “Si Diligis” Mass for Supreme Pontiffs. And when you think about it, this way of proceeding makes sense. It would be a form of suicide for anyone at the Vatican to issue express permission to go back on what has been pushed forward by a succession of popes and curial decrees; but by allowing restoration to spread unchecked, good things happen and no one is hurt.
On June 11, 2020, Fr. Zuhlsdorf wrote:
In 1986 the English edition of Joseph Ratzinger’s Feast of Faith was published by Ignatius Press. At the time, it was a bombshell of enormous importance. It is still extremely helpful in understanding the state of the Church in the world and is foundational in Ratzinger’s faith. In that volume the future Benedict XVI reflected on the feast of Corpus Christi, which held profound significance for him from his youth onward. His Holiness juxtaposed the sad decline of Eucharistic devotions after the Second Vatican Council with what the Council of Trent taught. Although the anti-triumphalism of some post-Conciliar liturgists had repressed Eucharistic exposition, adoration and processions,
(and now Fr. Z proceeds to quote Ratzinger): 
the Council of Trent had been far less inhibited. It said that the purpose of Corpus Christi was to arouse gratitude in the hearts of men and to remind them of their common Lord. (cf. Decr. desc. Euch., c. 5; DS 1644). Here in a nutshell, we have in fact three purposes: Corpus Christi is to counter man’s forgetfulness, to elicit his thankfulness, and it has something to do with fellowship, with that unifying power which is at work where people are looking for the one Lord. A great deal could be said about this; for with our computers, meetings and appointments we have become appallingly thoughtless and forgetful (pp. 128-9).
Let us consider Trent again for a moment. There we find the unqualified statement that Corpus Christi celebrates Christ’s triumph, his victory over death. Just as, according to our Bavarian custom, Christ was honored in the terms of a great state visit, Trent harks back to the practice of the ancient Romans who honored their victorious generals by holding triumphal processions on their return. The purpose of Christ’s campaign was to eliminate death, that death which devours time and makes us cultivate the lie in order to forget or “kill” time. … Far from detracting from the primacy of reception which is expressed in the gifts of bread and wine, it actually reveals fully and for the first time what “receiving” really means, namely, giving the Lord the reception due to the Victor. To receive him means to worship him; to receive him means precisely, Quantum potes tantum aude — dare to do as much as you can. (p. 130)
Lastly, St. John Henry Newman, in his Sermon Notes for the Sunday within the Octave of Corpus Christi (May 25, 1856, not intended for publication), expressed the following eminently Catholic sentiments, which we would do well to adopt and internalize once again as our own:
There is no feast, no season in the whole year which is so intimately connected with our religious life, or shows more wonderfully what Christianity is, as that which we are now celebrating [viz., Corpus Christi]…. The world is in wickedness. Satan is god of the world; unbelief rules. Now this opposition to us has a tendency to weigh us down, to dispirit us, to dull our apprehensions.… Now observe, How almighty love and wisdom has met this. He has met this by living among us with a continual presence. He is not past, He is present now. And though He is not seen, He is here. The same God who walked the water, who did miracles, etc., is in the Tabernacle. We come before Him, we speak to Him just as He was spoken to 1800 years ago, etc. Nay, further, He [does] not [merely] present Himself before us as the object of worship, but God actually gives Himself to us to be received into our breasts. Wonderful communion. This [is] how He counteracts time and the world. It [the Blessed Sacrament] is not past, it is not away. It is this that makes devotion in lives. It is the life of our religion. We are brought into the unseen world.
