Forget about the speculative attempts to uncover the "primitive" Roman Canon for a moment, and try to understand the apparent conceptual confusion of the prayer as it has been prayed for more than a millennium. One jumps from the "holy, unspotted" sacrifices in its opening words - before the words of consecration have been uttered - to the bestowal of the "good things" of creation at its close - after the words of consecration have been uttered - and wonders how it all fits together. One hears the word 'chiastic' mentioned with regards to its structure: i.e. its rationale is not linear, but rather the end parallels the beginning.
If one takes the text of the prayer, and lays it out in its twelve paragraphs, each allotted an equal width across a page turned 'landscape'-wise, counting the Qui pridie section and Simili modo as one single paragraph: just jotting down the headings will do for our purpose.... one notices that Qui pridie (the sixth paragraph) and Unde et memores (the seventh) form the two central sections. Then fold the two halves of the page together, and see what you get. The - let's call it 'thematic' - correspondence between the sections that now touch each other are fairly obvious.
Starting from the middle: (6) and (7) bring together Christ's acts with his words at the Last Supper. The Incarnate and Ascended Lord is the Holy Bread and the Cup of Salvation.
(5) and (8) are both prayers for acceptance of our offerings: one echoing the language of St Paul in the 12th chapter of the letter to the Romans, the other the great types of the Old Testament.
(4) and (9) are perhaps the least successful parallel of the series: the Hanc igitur is hardly a descending epiclesis in the same way in which the Supplices is (arguably) an ascending epiclesis... however it is worth noting that both of these paragraphs do mention the acceptance of the oblation, and also the request for deliverance from hell in (4) meets its opposition in the ascent to heaven in (9).
(3) and (10) are an obvious parallel: the Saints in light are juxtaposed with the faithful who have gone to their rest; and in (2) and (11) the Martyrs triumphant and the Church militant are placed side by side. The parallel is stronger if one takes the second part of the Te igitur (the prayer for the church) and adds that part of (1) onto (2).
That leaves the first part of (1) to be set alongside (12), which brings us back my original perplexity: what is the immaculate sacrifice doing at the beginning of the Canon? And why the gifts of creation at the end? Well, at least one can see now that there is a parallel between these two sections at the extremities, both of which ask for the acceptance of the gifts or sacrifices through Christ our Lord. And this parallelism may go some way to explaining the apparent dis-ordering of the prayers.
Whatever the original "primitive" ordering of the prayers, and whatever missing ritual (benediction of offerings made by the people on particular festivals perhaps?) that explains the prayer over the gifts of creation at its conclusion, a rationale for the current form seems to emerge by viewing the prayer as structurally chiastic. In fact, one wonders if it gained its form for this precise reason: did the prayer grow from second and even first Century tradition, until it was slightly adjusted, a few extra prayers or words added, to give it its present literary form in order to achieve this balance of juxtaposition of elements? This need not have been a consciously artistic process for the most part: a chiastic structure is for most people a very satisfying literary device, especially when its architecture includes various elements of simple parallelism and repetition, amplification, opposition and allusion - all of which the chiastic structure of the Roman Canon seems to encompass.
If we accept this as a reasonable theory for the coherence of the Roman Canon, as a non-linear literary structure, what does this do for the theology of the prayer? That is a question that I am totally incompetent to tackle - which is another way of saying that I would like to speculate about it in another post. And also - are there are any other patterns or symmetries within its structure?