Now that our hearts are filled with such beautiful and holy thoughts, nothing remains but to return thanks to God, the Author of all good things; thus the first Priest did, who before instituting the sacrament of the Holy Eucharist gave thanks to God his Father. So the celebrant, before the great prayer in the course of which he will consecrate the holy offerings, addresses to God this act of thanksgiving: “Let us give thanks to the Lord.” The faithful give their consent, saying: “It is meet and just.” Then the priest himself gives thanks to God, glorifying him, praising him with the angels, and thanking him for all the gifts which he has bestowed upon us from the beginning of time. Finally he recalls the ineffable and incomprehensible mystery of the Incarnation and Redemption; then he consecrates the offerings, and the sacrifice is complete.
How is this? The priest recites the story of that august Last Supper, telling how, before he suffered, he gave to the disciples this sacrament, and took the bread and the chalice, and having given thanks said those words which expressed the mystery; repeating those words, the celebrant prostrates himself and prays while applying to the offerings these words of the Only-Begotten, our Saviour, that they may, after having received his most holy and all-powerful Spirit, be transformed—the bread into his holy Body, the wine into his precious and sacred Blood.
When these words have been said, the whole sacred rite is accomplished, the offerings are consecrated, the sacrifice is complete; the splendid Victim, the Divine oblation, slain for the salvation of the world, lies upon the altar. For it is no longer the bread, which until now has represented the Lord’s Body, nor is it a simple offering, bearing the likeness of the true offering, carrying as if engraved on it the symbols of the Saviour’s Passion; it is the true Victim, the most holy Body of the Lord, which really suffered the outrages, insults and blows; which was crucified and slain, which under Pontius Pilate bore such splendid witness; that Body which was mocked, scourged, spat upon, and which tasted gall. In like manner the wine has become the blood which flowed from that Body. It is that Body and Blood formed by the Holy Spirit, born of the Virgin Mary, which was buried, which rose again on the third day, which ascended into heaven and sits on the right hand of the Father.
But how can we have faith to believe this?
He himself said: “This is my body. This is my blood.” He himself commanded the Apostles to do this, and through them, the whole Church. “Do this,” he said, “in remembrance of me.” He would not have given this command unless he had been going to give them the power to enable them to do this. What then is this power? It is the Holy Spirit, the power from on high which has strengthened the Apostles according to the words which the Lord spoke unto them: “But tarry in the city of Jerusalem, until ye be endued with power from on high.” Such is the work of that divine descent. For, once come down, the Holy Spirit did not forsake us, but he is with us, and he will remain until the end. It is for this purpose that the Saviour sent him, so that he may dwell with us for ever: “Even the Spirit of truth whom the world cannot receive, because it seeth him not, neither knoweth him: but ye know him; for he dwelleth with you, and shall be in you.” This is the Spirit who through the hand and the tongue of priests consummates the mysteries.
St Nicholas Cabasilas