While at first this prayer may sound confusing, it is not heretical. The unconsecrated bread and wine presented at the Offertory are offered up by the Church in thanksgiving "to the Creator for bread and wine, fruit of the ‘work of human hands,’ but above all as ‘fruit of the earth’ and ‘of the vine’—gifts of the Creator. The Church sees in the gesture of the king-priest Melchizedek, who ‘brought out bread and wine,’ a prefiguring of her own offering" (CCC 1333).
The USCCB’s "The Real Presence of Jesus Christ in the Sacrament of the Eucharist: Basic Questions & Answers" explains the use of symbolism when referring to the Eucharist:
Are the Consecrated Bread and Wine "Merely Symbols"?
In everyday language, we call a "symbol" something that points beyond itself to something else, often to several other realities at once. The transformed bread and wine that are the body and blood of Christ are not merely symbols because they truly are the body and blood of Christ. . . . At the same time, however, it is important to recognize that the body and blood of Christ come to us in the Eucharist in a sacramental form. In other words, Christ is present under the appearances of bread and wine, not in his own proper form. We cannot presume to know all the reasons behind God’s actions. God uses, however, the symbolism inherent in the eating of bread and the drinking of wine at the natural level to illuminate the meaning of what is being accomplished in the Eucharist through Jesus Christ.
There are various ways in which the symbolism of eating bread and drinking wine discloses the meaning of the Eucharist. For example, just as natural food gives nourishment to the body, so the Eucharistic food gives spiritual nourishment. Furthermore, the sharing of an ordinary meal establishes a certain communion among the people who share it; in the Eucharist, the people of God share a meal that brings them into communion not only with each other but with the Father, Son, and Holy Spirit. Similarly, as St. Paul tells us, the single loaf that is shared among many during the Eucharistic meal is an indication of the unity of those who have been called together by the Holy Spirit as one body, the body of Christ (1 Cor. 10:17). To take another example, the individual grains of wheat and individual grapes have to be harvested and to undergo a process of grinding or crushing before they are unified as bread and as wine. Because of this, bread and wine point to both the union of the many that takes place in the Body of Christ and the suffering undergone by Christ, a suffering that must also be embraced by his disciples. Much more could be said about the many ways in which the eating of bread and drinking of wine symbolize what God does for us through Christ, since symbols carry multiple meanings and connotations.
Additional excerpts may be found at www.usccb.org/publishing.