This is new content in the second edition of Praying the Mass: The Prayers of the People, Chapter 9, "Offertory Prayers".
An external act which represents an internal reality is empty unless that internal reality is truly present. Imagine a man giving his wife a bouquet of roses, a gesture generally recognized as a display of love, without actually caring about her at all. The roses are real, the wife’s reaction is real, but there is something missing: the intention. This analogy can be applied to the Offertory Procession, when bread and wine are brought to the priest. This external act, often carried out by members of the congregation, is not a mere functional procedure; it is representative of so much more.
In the ancient Church, the bread and wine would often be personally supplied by members of the faithful. Nowadays, the bread and wine are usually purchased by with parish funds (which ultimately come from the faithful), so they still represent our offering, our presentation to the Lord. This presentation is an external manifestation of the internal self-offering which we are called to make during the Mass: the bread and wine are not just the necessary matter for celebrating the Eucharist, they also represent all that we have to offer to God. Pope John Paul II, in his 1980 letter to Bishops on the Eucharist, explained this rite’s significance:
Although all those who participate in the Eucharist do not confect the sacrifice as [the priest] does, they offer with him, by virtue of the common priesthood, their own spiritual sacrifices represented by the bread and wine from the moment of their presentation at the altar. … The bread and wine become in a sense a symbol of all that the eucharistic assembly brings, on its own part, as an offering to God and offers spiritually. (Dominicae Cenae 9)
Just as the bread and wine are presented to the priest who offers them to God, we offer ourselves to God as a spiritual sacrifice by virtue of our baptismal priesthood. Archbishop Fulton J. Sheen, in his 1936 missal companion Calvary and the Mass, wrote about this self-offering:
We are therefore present at each and every Mass under the appearance of bread and wine, which stand as symbols of our body and blood. We are not passive spectators as we might be watching a spectacle in a theater, but we are co-offering our Mass with Christ. [We] offer ourselves in union with Him, as a clean oblation to the heavenly Father. (The Offertory)
The only sacrifice that is truly acceptable to God the Father is the Eucharist, which is the very Body, Blood, Soul, and Divinity of His Son, our Lord Jesus Christ. But God looks on what we offer with fatherly affection. The bread and wine presented to Him by the priest is deemed acceptable as the means by which He will give us the Eucharist; the bread and wine are gifts from God to begin with. Because the bread and wine represent our spiritual sacrifices, these too are regarded with a similar love: God knows what He will make of the bread and wine, and He knows what He will make of our meager sacrifices.
Once the bread and wine have been placed on the altar, the priest prepares them for the Eucharistic Prayer and prays over them.