In order to apply the merits of redemption to our souls we must recapitulate in ourselves the death to sin which was brought about on the Cross. Hence, the first act is the offering of ourselves in union with Christ. In the early Church this was done by offering the very same elements which Our Lord Himself offered at the Last Supper; namely, bread and wine. In the early Church the faithful brought bread and wine to the Mass and some of each was used by the priest for the sacrifice.
There are some intrinsic reasons why these elements should have been used, even apart from their Divine authorization. First, bread and wine had been the traditional nourishment of most men through history. Bread, as it were, is the very marrow of the earth and wine is as its very blood. The faithful, therefore, in offering that which has given them their physical sustenance and life, are equivalently giving themselves.
A second reason is that no two substances in nature better represent unity than do bread and wine. Bread is made from a multiplicity of grains of wheat, wine from a multiplicity of grapes. So the faithful, who are many, combine to make one offering with Christ.
A third reason is that few elements in nature better symbolize sacrifice than wheat and grapes. Wheat does not become bread until it has passed through the Calvary of a winter and has been subjected to the tortures of the mill. Grapes do not become wine until they have trodden the Gethsemane of the wine press. Today, the faithful no longer bring bread and wine to the Sacrifice of the Mass but they bring the equivalent; that is the reason why the collection is often taken up at what is called the Offertory of the Mass. The material sacrifice which they make for the Mass is still a symbol of their spiritual incorporation in the death of Christ. Though they bring no bread and wine, they bring that which buys bread and wine, and these elements still represent the material of their united sacrifice.