Monsignor Ronald Knox remarks in mass in slow motion that the Mass is a continuous action and that "The sacrifice is going on all the time, not just at odd intervals". He further suggest that the sacrifice is being made from the offertory to the reception of Holy Communion. Even before the consecration when the bread and wine are changed into the body and blood of Christ, we (or the priest on our behalf) is offering the sacrifice. After the priest has washed his hands he extends his hands to the people and says: "Pray, brethren, that our sacrifice may be acceptable to God, the Almighty Father". To which the people respond: "May the Lord accept the sacrifice at your hands for the praise and glory of His name, for our good and the good of all His Church."
Ordinarily we think of the canon of the mass (the Eucharistic Prayer) as the beginning of the offering of the sacrifice. And even more particularly that Christ is first made present at the consecration and then is offered to the Heavenly Father. However, the words and action of the mass suggest that the sacrifice of the mass is a continuous action which is achieved at the consecration and continues to be offered in the Eucharistic Prayer following the consecration.
The Offertory begins when the bread and wine are brought up to the Altar and received by the priest. The monetary gifts are also received at this time. Both the bearers of the gifts and the gifts themselves represent us. Bishop Sheen expresses the nature of this self-sacrifice in his book, "This is the Mass":
There are some intrinsic reasons why these elements should have been used, even apart from their divine authorization.
First, the 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 not no 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..." What Bishop Sheen so beautifully and poetically expresses in this quote is the reality of the mass as Christ's sacrifice and ours. We offer with Him to the Father our bodies, minds and hearts. We offer our will and imagination. We offer to him what is both bitter and sweet to us. We offer the ordinary and the momentous occurrences of our lives. Monsignor Knox remarks that we should in imagination put ourselves on the paten next to the host when the priest lifts the paten and prays: "Blessed are you God of all creation, through your goodness we have this bread to offer..." And as someone said to me recently we should put ourselves and others in the chalice when the priest lifts it up and prays: "Blessed are you, God of all creation, through your goodness we have this wine to offer..."
We are setting aside not only the bread and wine for consecration but also ourselves. We are praying for our transformation more and more into the Mystical Body of Christ, His Church.