In the ancient Gelasian Sacramentary today’s Collect was used on the Friday after Quinquagesima. I assume it was dragged into Lent because of the themes present in the vocabulary.
However, the redactors of the Novus Ordo made a substitution. They substituted observatio for ieiunium.
COLLECT
Da, quaesumus, Domine, fidelibus tuis
observationi paschali convenienter aptari,
ut suscepta sollemniter castigatio corporalis
cunctis ad fructum proficiat animarum.
In the so-called Veronese Sacramentary, also revealing ancient Roman usage, we have interesting differences. In the prayers during September we find: Tribue, quaesumus, domine, fidelibus tuis, ut ieiuniis paschalibus convenienter aptentur, et suscepta sollemniter castigatio corporalis ad fructum cunctis transeat animarum. So, today’s prayer is certainly Roman in its expression. It is closer to that of the pre-Lenten Quinquagesimal oration in the Gelasian Sacramentary. It is also not unlike the Collect for Saturday after the 2nd Sunday of Lent in the 1962MR but a close match is not to be found in the pre-Conciliar Missale Romanum.
So, why substitute ieiunium with observatio??
What is going on?
Our brilliantly assembled Lewis & Short Dictionary lets us in on the fact that observatio means, in the first place, “a watching, observing, observance” and thereafter “an office, duty, service” in ecclesiastical Latin. Perhaps “observance” is the best way to get at the moral dimension of the word. The dictionary of liturgical Latin Blaise suggests that a good way to render apto “interiorly dispose”. That sounds right to me. The concept of aptum with pulchrum in Latin thought (from rhetoric), is profound, but my time here is short. It is all part of decorum theory: that which is fitting, suitable, even beautiful. Consistent with this concept inhering in the prayer is the adverb convenienter, which is “fitly, suitably, conformably, consistently (synonyms: congruenter, constanter“.
One gets the sense of an over all theme to the prayer today.
Castigatio, which concept is now familiar from the prayers of this last week, is “a correcting, chastising, punishment, correction”. We used to use the word castigatio and related forms for the correction of our Latin homework.
A deep word, and one explored much by the late Pope John Paul II in his early writings about the dignity of the human person, is fructus, from the verb fruor. Fruor, one of the words which goes with the ablative, is “to derive enjoyment from a thing, to enjoy, delight in (with a more restricted meaning than uti, ‘to make use of a thing, to use it’).
Sollemniter is a very cool word. It is an adverb from sollemnis. Sollemnis has to do with the sun, sol. Thus, sollemnis points to an annual event, something appointed to take place, such as a festival or sacrifice or games in honor of the gods. Thus it also signifies usual or customary religious ceremonies. Sollemniter has a deep religious overtone to it in which one needs to hear an echo of the earth whirling around the sun.
LITERAL TRANSLATION
We beseech (You), O Lord, grant to Your faithful
to be interiorly disposed for the paschal observance in the fitting way,
so that the stern bodily correcting which has been solemnly undertaken
may be advantageous for all unto the intended fruitful benefit of souls.
Think of the Gospel phrase, “you know a tree from its fruit”. The tree produces something of value by which it can be judged. The tree is apt for the sake of a good outcome, a reason to be. The tree is suitable for its final goal, its purpose for existing, when it bears fruit which is destined for our enjoyment. This is more than just use, since it points to the proper end, the good end and purpose for which the fruit is destined.
“Use” in the sense of utor can be neutral. When it concerns moral issues, mere utor can be negative, since it doesn’t consider the deeper dimension of the final cause (to use philosophical language). 
Fruor, on the other hand, connects enjoyment with “use”, in the sense of a harmony between the final end of the thing and the reason why we as subjects of actions are involved with the thing in question. This enters into human relationships.
The late Pope wrote about relations between men and women, making the distinction that one cannot “use” someone else in the sense of utor because that other person is the dignified subject of actions. The other person cannot be reduced to the object of actions in the sense of utor. Fruor, however, can take into consideration the other person’s final end and reason for being.
Today, our fructus isn’t quite so involved, but it nevertheless points to the fact that what we do during Lent has a reason behind it, or rather in front of it. To neglect this reduces the observance of Lent to something empty, a formal practice without any real reason. One might think of “cultural Catholicism” in this light.
We return to the question above. So, why substitute ieiunium with observatio?? What is going on?
It just occurred to me that Pope Paul VI in 1966 published an Apostolic Constitution (the most weighty legal document a Pope promulgates). It was called “Paenitemini” and it concerned how and why Catholics were to practice penance and mortifications.
With Paenitemini Paul VI shifted the emphasis of penance from physical practices to also an interior spirit of penance. Some criticize this move, since it is human nature to be lazy in this regard. In relaxing the emphasis on physical penance, fasting and abstinence, the impression was given that Catholics don’t have to do penance any more. Mind you, Paenitemini still imposes obligations, but there is a clear shift in the document. Furthermore, Paul VI provides for commuting or dispensing penance more widely.
You decide.
NEW CORRECTED ICEL VERSION:
Grant that your faithful, O Lord, we pray,
may be so conformed to the paschal observances,
that the bodily discipline now solemnly begun
may bear fruit in the souls of all.
And I am not making this up.
LAME-DUCK ICEL:
Lord,
may our observance of Lent
help to renew us and prepare us
to celebrate the death and resurrection of Christ.
Today’s prayer is unchanged from the Veronese Sacramentary and the Gelasian and so-called “Gregorian“.
One of the meanings of secundum found in the prestigious Lewis & Short Dictionary is “agreeably to, in accordance with, according to”. Largire is an imperative of a deponent verb, not an infinitive. The famous verb cogito is more than simply “to think”. It reflects deeper reflection, true pursuit in the mind: “to consider thoroughly, to ponder, to weigh, reflect upon, think”.
