I’ve nothing to add to Kosta’s fine explanation save these words from the Divine Liturgy of +John Chrysostomos, called the “epiklesis” when the change actually takes place. Note that it is the Holy Spirit Which makes the change, not the priest:
“Priest (in a low voice):
Once again we offer to You this spiritual worship without the shedding of blood, and we ask, pray, and entreat You: send down Your Holy Spirit upon us and upon these gifts here presented.
And make this bread the precious Body of Your Christ.
(He blesses the holy Bread.)
Deacon (in a low voice):
Amen.
Priest (in a low voice):
And that which is in this cup the precious Blood of Your Christ.
(He blesses the holy Cup.)
Deacon (in a low voice):
Amen.
Priest (in a low voice):
Changing them by Your Holy Spirit.
(He blesses them both.)
Deacon (in a low voice):
Amen. Amen. Amen.
Priest (in a low voice):
So that they may be to those who partake of them for vigilance of soul, forgiveness of sins, communion of Your Holy Spirit, fulfillment of the kingdom of heaven, confidence before You, and not in judgment or condemnation. Again, we offer this spiritual worship for those who repose in the faith, forefathers, fathers, patriarchs, prophets, apostles, preachers, evangelists, martyrs, confessors, ascetics, and for every righteous spirit made perfect in faith....”
In fact, that would be appropriate to speak to the Latin Eucharistic Prayer, which largely says the same thing (in a different light):
Father, you are holy indeed, and all creation rightly gives you praise. All life, all holiness comes from you through your Son, Jesus Christ our Lord, by the working of the Holy Spirit. From age to age you gather a people to yourself, so that from east to west a perfect offering may be made to the glory of your name.And so, Father, we bring you these gifts. We ask you to make them holy by the power of your Spirit, that they may become the body and blood of your Son, our Lord Jesus Christ, at whose command we celebrate this eucharist.
On the night he was betrayed, he took bread and gave you thanks and praise. He broke the bread, gave it to his disciples, and said:
Take this, all of you, and eat it: this is my body which will be given up for you.
When supper was ended, he took the cup. Again he gave you thanks and praise, gave the cup to his disciples, and said:
Take this, all of you, and drink from it:
this is the cup of my blood, the blood of the new and everlasting covenant. It will be shed for you and for all so that sins may be forgiven. Do this in memory of me.
Different words...but largely the same content. The epiklesis in the Latin (novus ordo) liturgy is italicized.
Yep, agree.