The early Church developed a fairly uniform Eucharistic prayer or anaphora (“offering”). These anaphora could be divided into: 1) introductory dialogue (our Great Thanksgiving); 2) preface (unique for each Sunday of the church year); 3) Sanctus (“Holy, Holy, Holy...”); and 4) anamnesis (an all but untranslatable Greek word which means a past event that is made present here and now). Usually Christ’s passion, resurrection, and ascension are “brought to the present”. The words of institution (the “moment of consecration” in Catholicism when the bread/wine become the body/blood of Christ) are in the anamnesis. The invocation of the Holy Spirit, or epiclesis, is the “moment of consecration” in Orthodox Churches. An epiclesis was not present in Roman or Anglican anaphora, but it has been in all Episcopal anaphora since 1789. This may be because Samuel Seabury (the first American bishop) was consecrated by Scottish bishops whose anaphora contained an epiclesis. Many Episcopal theologians believe that the entire anaphora taken as a whole completes the consecration. In this theology, the congregation robustly completes the anaphora said for them by the celebrant with the Great AMEN (printed in the Book of Common Prayer in all capital letters to encourage enthusiasm).
~Dr Gil Haas