Father Hugh Barbour – Catholic Answers Article –
Why did our Savior give us the sacrament of his body and blood?
First of all, so that we would be able to offer—throughout time until he comes again on the last day—the same sacrifice he offered on the wood of the cross, so that the same fruits of his saving offering should be applied to the souls of Christ’s members each day and in every age.
We were not to repeat this sacrifice in its natural, “bloody” offering, however, but under signs of bread and wine as both sacrifice and spiritual food. Our Lord first offered his body and blood under these signs at the Last Supper, even before he offered them in their natural forms and appearances in his Passion. Thus the Mass is not only Calvary: it is a repetition of what the Lord did at the Last Supper in the Cenacle on Mount Sion in Jerusalem on the night before he suffered.
This is the “mystery of faith” we profess and adore and receive. The very same body and blood of the Lord present in one heavenly place in his natural dimensions is also really and substantially present wherever the sacrament is present. This is a marvel beyond the comprehension of any mind, human or angelic. What it means is that there is a hidden and mysterious proportion between the natural body and blood of the Lord and the Eucharist on our altars such that wherever the sacred appearances of bread and wine are there, he is there as truly as any of us are physically present to each other.
The Blessed Sacrament is a symbol, but of a very perfect and intense kind. It is not a mere symbol, but actually contains the things it symbolizes. It is the body and blood of the Lord, it is the sacrifice of the same body and blood. Bread and wine are no more, but only their outward appearances in the place occupied by their sensible forms.