The Responsorial (Psalm 66) alerts us to the greatness of the mystery of God’s promises and their fulfillment:
“Blessed be God who filled my soul with fire.”
In Deuteronomy 34:1-12 God is about to fulfill the promise he made to give his People the “land which I swore to Abraham, Isaac and Jacob that I would give to their descendants.” But the one who would lead them into it was Joshua. He was “filled with the spirit of wisdom, since Moses had laid his hands on him.” Still in our day, the Church “lays hands” on those perceived to be chosen for a special work, and “calls down” the Spirit upon them.
In the Eucharistic Prayer, after “naming” God as holy, the Church “calls down” the Spirit on the gifts of bread and wine, asking God to change them into Christ’s Body and Blood. The word for this “calling down” is epiclesis. In the Epiclesis, we ask God to fulfill Christ’s promise to the Church:
I am the living bread that came down from heaven. Whoever eats of this bread will live forever; and the bread that I will give for the life of the world is my flesh.
This is the ultimate fulfillment of God’s preliminary promise to his People:
I have observed the misery of my people... and I have come down to deliver them... and to bring them up... to a good and broad land, a land flowing with milk and honey. 
Eucharist is a sign and foretaste of the true and ultimate “Promised Land” — which we call now the “wedding banquet of the Lamb.”
In Matthew 18:15-20 Jesus speaks in preview of the Church upon whom Christ “sent down” the Holy Spirit at Pentecost. He tells his disciples, “If two of you join your voices on earth to pray for anything whatever, it shall be granted you by my Father in heaven.”
The reason why the bread and wine change into the Body and Blood of Christ at Mass is because, in the Epiclesis, the whole Church together is asking for it. It is not because the presiding priest has some special power from Holy Orders that give to his words the power of a magic spell — which, frankly, is what most of us grew up believing. The prayer of the presider has no more effect on the bread and wine than anyone else’s prayer. His role is to make the bishop present. That makes the prayer of the people at Mass the prayer of the whole Church throughout the world. Where the bishop is, his church is. Where one bishop is with his church, the churches of all the bishops are present: the whole Church. Jesus said, “Where two or three are gathered in my name, I am there in their midst.” How much more so when the whole Church assembles as one in the Holy Spirit?
Initiative: Be a priest. Unite yourself to Christ, the presider, the bishop and the whole church at Mass.
 Read all of John 6:29-59. Then Exodus 3:7-8.
 Luke 24:49; John 20:22; Acts 8:14-17, 9:17, 19:1-6.
 General Instruction for the Roman Missal, no. 4: “The celebration of the Eucharist is the action of the whole Church.” 91: “Every authentic celebration of the Eucharist is directed by the Bishop, either in person or through the priests, who are his helpers.” (References. to Vatican II, “The Church,” nos. 26,28; and “Liturgy” no. 42). And see Matthew 18:18-20.
Even if a priest celebrates Eucharist alone (forbidden by Canon Law 906 unless for a “good and reasonable cause”), the whole Church celebrates with him. Without an ordained priest there can be no Eucharist, because the bishop is not present making the congregation’s prayer the prayer of the whole Church.