As I mentioned a week or more ago, I was quite surprised to find that in Scotland, when at the Ordinary Form of Mass, I went to stand at the Orate fratres, as here in Australia we have all been catechised to do (pursuant to the rubricks of the latest edition of the Roman Missal), instead everybody knelt! They remained kneeling till after the Amen concluding the Eucharistic Prayer.
In other parts of the world, at the modern Mass, the people stand for the Orate fratres, or at least after it has concluded (as was the practice here until the last few years), and likewise for the Prayer over the Gifts (Oratio super oblata), and for the Sursum corda dialogue, and for the Preface and Sanctus. Only then do the people kneel: in English-speaking countries, for the whole of the Eucharistic Prayer, as our bishops ruled at the time of the liturgical reform; according to the universal norms, for the Consecration alone.
Compare these variants to the practices at the Extraordinary Form of Mass, according to the customs I am familiar with: at High Mass, the people, having sat during the Offertory (except in Bavaria, where they knelt) stand at the ecphonesis of the Secret (the Oratio super oblata, which in the Traditional Mass is said sotto voce until its end), remain standing for the ensuing dialogue and the Preface, then kneel as soon as the Sanctus is begun; while instead, at Low Mass, the people remain sitting, then kneel at the Sanctus.
Now, whatever of the older form of the liturgy, I return to the Institutio Generalis Missalis Romani, according to the 3rd typical edition of 2002, and quote from n. 43:
Fideles stent ab initio cantus ad introitum, vel dum sacerdos accedit ad altare, usque ad collectam inclusive; ad cantum Allelúia ante Evangelium; dum ipsum Evangelium proclamatur; dum professio fidei et oratio universalis fiunt; necnon ab invitatorio Oráte fratres ante orationem super oblata usque ad finem Missae, praeter ea quae infra dicuntur.
Sedeant autem dum proferuntur lectiones ante Evangelium et psalmus responsorius; ad homiliam et dum fit praeparatio donorum ad offertorium; atque, pro opportunitate, dum sacrum silentium post Communionem servatur.
Genuflectant vero, nisi valetudinis causa, vel ob angustiam loci vel frequentiorem numerum adstantium aliasve rationabiles causas impediantur, ad consecrationem. Hi vero qui non genuflectunt ad consecrationem, inclinationem profundam peragant dum sacerdos genuflectit post consecrationem.
Est tamen Conferentiae Episcoporum, gestus et corporis habitus in Ordine Missae descriptos ingenio et rationabilibus populorum traditionibus ad normam iuris aptare. Attendendum tamen erit, ut sensui et indoli cuiusque partis celebrationis respondeant. Ubi mos est, populum ab acclamatione Sanctus expleta usque ad finem Precis eucharisticae genuflexum manere, hic laudabiliter retinetur.
Ad uniformitatem in gestibus et corporis habitibus in una eadem celebratione obtinendam, fideles monitionibus obtemperent, quas diaconus, vel minister laicus, vel sacerdos durante celebratione proferunt, iuxta ea quae in libris liturgicis statuuntur.
The first paragraph tells us, inter alia, that the people stand from the Orate fratres until the end of Mass, except at those parts noted further on - which the second and third paragraphs explain to be two places: at the consecration, all kneel, unless unable to do so by some reasonable cause (in which case one bows profoundly); and during the silence after communion, one may sit.
The fourth paragraph explains that bishops' conferences may adapt these rules to fit the customs of their people - in particular, the Instruction notes that "Where it is the custom for the people to remain kneeling from the Sanctus acclamation until the end of the Eucharistic Prayer, this may praiseworthily be retained": in other words, if it is the norm to kneel for the whole of the Eucharistic Prayer, what a laudable and admirable rule to maintain! (This is the case, so far as I know, throughout the Anglosphere.)
The fifth and last paragraph notes that, when the priest, deacon or lay minister tells the people to stand, sit or kneel according to the rules laid down, it is for the people to follow their bidding. But note that they should obey only when they are told to do what they should! (Obviously if they are told to stand on their heads during the Canon, this would be a foolish violation of the rubricks, to be laughed off.)
But why this change in the modern Mass, from standing after the Orate fratres to standing at the Orate fratres? I was told (by a bishop, if I recall correctly) that the reason is that some dissenting Catholics in Germany were entirely omitting the Orate fratres, so as to further downplay the doctrine of the Sacrifice of the Mass; and that to re-affirm both the phrase and its important declaration of true teaching, the Vatican decided to forcibly emphasise it by having the people stand at this versicle and response, which is such an urgent plea - not just Oremus, "Let us pray", but Orate fratres, "Pray, brethren!" - that so concisely reiterates the doctrine of the Mass as a Sacrifice acceptable to God the Father, offered by the priest, the people assisting and co-offering at his hands, not merely for God's glory, but to obtain all benefits for ourselves and Holy Church:
Orate, fratres, ut meum ac vestrum sacrificium acceptabile fiat apud Deum Patrem omnipotentem.
Suscipiat Dominus sacrificium de manibus tuis, ad laudem et gloriam nominis sui, ad utilitate quoque nostram, totiusque Ecclesiæ suæ sanctæ.
So, why is it that in Australia, in the United States, and in England too (as I have observed personally), that this new rule of standing at the Orate fratres has been brought in, whereas in Scotland the people kneel instead, and in Italy they keep the slightly older practice of standing after the Orate fratres?
The Scottish posture at the modern Mass at this point must surely be one of those local adaptations permitted in the fourth paragraph mentioned above - I would be interested to have confirmation of this...
It seems to me that it is a question of due catechesis and instruction having been undertaken in the first three countries mentioned, informing the people of this modification; whereas in Italy, despite eight years having passed, no one seems aware of this - even in St Peter's itself, where I was amazed to see, at a Papal Mass I attended back in September, that this rule was even now not yet observed!
The annoying thing about the post-Conciliar Church is that there is a great spirit of sloppiness and neglect of any and all instructions.