The essential difference between the Offertory Rite in the Extraordinary Form of the Mass, and that ("the Preparation of the Gifts") in the Ordinary Form, is the degree of prolepsis.
Prolepsis - strange word! What does it mean? It means a "foreshadowing", a "foretelling", an anticipation (deriving from the Greek verb προλέγω).
We know – as Bishop Elliott reminded us in one of his liturgical handbooks – that the Mass is not a cereal sacrifice. Furthermore, there is no oblation of bread and wine as such, since clearly such offerings cannot placate the Almighty. Only insofar as the bread and wine will become the Body and Blood of the One Priest and Victim, Christ Jesus, the Lamb once slain Who lives for ever, do they have value: thus, anticipating their transformation into His Flesh and Blood Most Precious, already at the Offertory they are offered up.
This explains the language used in the Traditional Offertory prayers over the bread and wine and both together – in the Suscipe sancte Pater, the Offerimus tibi Domine, and the Suscipe sancta Trinitas. The bread and wine are spoken of as already: the "spotless host" offered for all Christians, living and dead, that it profit unto salvation; the "chalice of salvation" whose sweet savour may ascend unto the Lord to avail for the salvation of the whole world; as "this oblation" offered to the Trinity in memory of Christ's saving works, honouring the saints and availing unto our salvation. It would make no sense to speak of the bread and wine, before the consecration, in such terms except precisely proleptically.
Whence comes this language of prolepsis? From the language of the Roman Canon itself: at its outset, long before the consecration of the elements by the very Words of the Lord (Verba Domini), the bread and wine are spoken of as hæc dona, hæc munera, hæc sancta sacrificia illibata ("these gifts, these presents, these holy unsullied sacrifices") and as hanc... oblationem, "this oblation".
The Offertory Rite, as the mediævals perceived, is thus already an anticipated doublet of the Canon of the Mass – which is why it was known then as the Canon minor.
The modern Mass, on the other hand, shies away from such full-blooded words. This reflects the "problem" that theologians of the fifties and sixties had with prolepsis – despite it having been the norm in the Church for many centuries, in the Eastern Rites no less than in the Western. (Indeed, the Mozarabic Rite is if anything the most proleptic of all, since its elaborate intercessions are offered up, speaking of the sacrifice of the Mass, long before the Preface and Consecration is reached.)
What to substitute for the old prayers? Bugnini reports in his long apologia for the reform of the liturgy that at one stage, various Scriptural passages were suggested as possible for praying while the bread and wine were readied, such as "Wisdom hath built herself a house, she hath hewn her out seven pillars. She hath slain her victims, mingled her wine, and set forth her table." (Wisdom ix, 1-2) Then someone had the bright idea of adapting the Jewish table blessings of bread and wine, much as, just perhaps (who can say?), Our Lord did at the Last Supper. We therefore bless the Lord God of all things for the bread and wine we have to offer (that controversial word "offer" was retained), the produce of plants and of human effort (how didactic!), which will become – what?
It was decided that, unlike in the Ambrosian Rite, to pray directly and in anticipation of the epiclesis that the elements be transsubstantiated would be to anticipate too much (that dratted prolepsis again!), so instead, two poetic phrases were used: "bread of life" and "spiritual drink". ("Spiritual drink" sounds very meagre, almost risible, in English: whisky is a spirit that we drink, for instance!) Many commentators have noted that unfortunately (or ecumenically!) these phrases are rather equivocal, neither affirming nor denying the total change of the substance of bread and wine into the Body and Blood.
What has been lost? There is now, in the Ordinary Form, no prayer in the Preparation of the Gifts offering them for such determinate ends, anticipating the offering up of the Divine Victim to compass our salvation and deliverance from our sins and all other blessings. What remains? The Orate fratres and its response, the Suscipiat. This is a very important prayer: the priest asks the people to pray that the sacrifice that he offers, and that they offer up in union with him, may be acceptable to the Lord, that it may indeed be a true and saving satisfaction and impetration. The people's response, to the effect that they beg God accept the offered sacrifice, to His praise and glory, and to benefit them and all the holy Church, does teach the truth of the Sacrifice.
The Novus Ordo also, it must be remembered, still retains the In spiritu humilatis, quoting from Daniel iii, 39-40, wherein the priest prays that (as new ICEL puts it), "With humble spirit and contrite heart may we be accepted by you, O Lord, and may our sacrifice in your sight this day be pleasing to you, Lord God." It is important that sacrificium nostrum... placeat tibi, Domine Deus be read in the strongest sense, as praying that the sacrifice offered – which is Christ – please the Lord, placate Him, appease Him, be a propitiation availing for us men and for our salvation. Undeniably, however, this is doctrine is deëmphasised in the modern Liturgy relative to the old.
A secondary difference is the degree of what might be called (by moderns) "uncomfortable words", relating to sinfulness and unworthiness. In the Old Mass, the priest offers the host as a propitiation "for my innumerable sins and offences and negligences" – such a prayer is well-nigh unimaginable in the sunny New Mass! Yet, strange to say, events of recent times have revealed that priests might well need to beseech forgiveness "for innumerable sins and offences and negligences" - can anyone dispute this, after so many scandals, "so much filth in the Church" as the Pope himself said, yea, as he has just said during his visit to Fatima, the greatest enemies of the Church are the sins of her members!
The Supreme Pontiff formerly known as Cardinal Ratzinger mentioned, while yet in that rank, that Gaudium et spes has passages that sound almost semi-Pelagian in their overconfident view of "modern man". It is evident that this hubristic spirit is not absent from the liturgy drawn up by those too-optimistic men of the sixties...
Let us be clear, it is worse than foolishness, it is wilful blindness, to speak not of the need to offer God sacrifices in reparation "for... sins and offences and negligences" – are we to continue the pretence that "all is calm, all is bright" and still smile pathetically at Mass, "fiddling while Rome burns"?
Again, though, I must be fair, and note that the priest in the Ordinary Form, while washing his hands, prays the Lava me – "Wash me, Lord, from my iniquity and cleanse me from my sin" (Psalm 50:4) – so the sense of sin is not entirely lacking in the modern Mass.
Note well: throughout this post I have left the Secret or Prayer over the Gifts out of the discussion! I well know that this ancient prayer is the very soul of the offertory, since it existed before any other offertory prayers at all were developed and added. But as to whether the emphasis of the doctrine it conveys has changed in the development of the modern Missal, that is a more complex topic, requiring much careful analysis...