It is not the power of man which makes what is put before us the Body and Blood of Christ, but the power of Christ Himself who was crucified for us. The priest standing there in the place of Christ says these words but their power and grace are from God. ‘This is My Body,’ he says, and these words transform what lies before him. (St. John Chrysostom, “Homilies on the Treachery of Judas”)Â
Hallowedground 
Thank you for the quote from St. John Chrysostom Ken. It shows that the teaching of the priest as alter Christus is not medieval as some would claim.
Father, The link on the post goes to a site citing many Early Fathers of the Church on the Eucharist, and other very Catholic things.