Yes, the epiclesis is absolutely necessary.
Orthodoxy insists that basically the entire liturgy up to and including the epiclesis is what effects the change, and would of course count the "words of institution" as being a very central part of that movement.
Excellently well said!
In The Anaphora of St. James it is obvious that both the words of Institution and the Epiclesis are included. The Church Fathers insisted on both, including Pope St. Gregory the Great (Gregory I, died 604 A.D.) who modeled what came later to be called the Tridentine Rite Mass after the Liturgy of Jerusalem (i.e. the Liturgy of St. James, including his Anaphora shown below). Pope St. Gregory also insisted (and this was totally in keeping with the ancient liturgies as well) that the Our Father be included in the place of honor. In all the liturgies east and west throughout the centuries this Ã¢â‚¬â€œ The Our Father, the Offertory (as is even especially shown forth in the Didache), the Words of Institution and the Epiclesis are included as the way the Eucharist is offered. Communion Prayers are, of course, ancient and venerable. The Tridentine form including Ã¢â‚¬Å“come Holy Spirit Sanctifier bless these giftsÃ¢â‚¬Â as the Epiclesis, has lasted up to the present but is not in the Novus Ordo.
The Anaphora of St. James:
The People: It is becoming and right.
Then the celebrant prays: Verily it is becoming and right, proper and due to praise Thee, to sing of Thee, to bless Thee, to worship Thee, to glorify Thee, to give Thee thanks, Maker of every creature visible and invisible, the treasure of eternal good things, the fountain of life and immortality, God and Lord of all:
Whom the heavens of heavens praise, and all the host of them; the sun, and the moon, and all the choir of the stars; earth, sea, and all that is in them; Jerusalem, the heavenly assembly, and church of the first-born that are written in heaven; spirits of just men and of prophets; souls of martyrs and of apostles; the six-winged seraphim, which cover their faces with two wings, their feet with two, and with two they fly, crying one to another with unresting lips, and the many-eyed cherubim, lordships, archangels, authorities, dread powers and angels with unceasing praises:
(Aloud.) With loud voice singing the victorious hymn of Thy majestic glory, crying aloud, praising, shouting, and saying:-
The People: Holy, holy, holy, O Lord of Sabaoth, the heaven and the earth are full of Thy glory. Hosanna in the highest; blessed is He that cometh in the name of the Lord. Hosanna in the highest.
The celebrant, making the sign of the cross on the gifts, says: Holy art Thou, King of eternity, and Lord and giver of all holiness; holy also Thy only-begotten Son, our Lord Jesus Christ, by whom Thou hast made all things; holy also Thy Holy Spirit, which searches all things, even Thy deep things, O God: holy art Thou, almighty, all-powerful, good, dread, merciful, most compassionate to Thy creatures; who didst make man from earth after Thine own image and likeness; who didst give him the joy of paradise; and when he transgressed Thy commandment, and fell away, didst not disregard nor desert him, O Good One, but didst chasten him as at merciful father, call him by the law, instruct him by the prophets; and afterwards didst send forth Thine only-begotten Son Himself, our Lord Jesus Christ, into the world, that He by His coming might renew and restore Thy image;
Who, having descended from heaven, and become flesh of the Holy Spirit and Virgin Godmother Mary, and having sojourned among men, fulfilled the dispensation for the salvation of our race; and being about to endure His voluntary and life-giving death by the cross, He the sinless for us the sinners, in the night in which He was betrayed, nay, rather delivered Himself up for the life and salvation of the world,
Then the celebrant holds the bread in his hand, and says: Having taken the bread in His holy and pure and blameless and immortal hands, lifting up His eyes to heaven, and showing it to Thee, His God and Father, He gave thanks, and hallowed, and brake, and gave it to us, His disciples and apostles, saying:-
(here break the bread)
The Deacons say: For the remission of sins and life everlasting.
Then he says aloud: Take, eat: this is my body, broken for you, and given for remission of sins.
The People: Amen.
Then he takes the cup, and says: In like manner, after supper, He took the cup, and having mixed wine and water, lifting up His eyes to heaven, and presenting it to Thee, His God and Father, He gave thanks, and hallowed and blessed it, and filled it with the Holy Spirit, and gave it to us His disciples, saying, Drink ye all of it; this is my blood of the new testament shed for you and many, and distributed for the remission of sins.
The People: Amen.
The celebrant: This do in remembrance of me; for as often as ye eat this bread, and drink this cup, ye do show forth the LordÃ¢â‚¬â„¢s death, and confess His resurrection, till He come.
The Deacons say: We believe and confess:
The People: We show forth Thy death, O Lord, and confess Thy resurrection.
The celebrant (Oblation): Remembering, therefore, His life-giving sufferings, His saving cross, His death and His burial, and resurrection from the dead on the third day, and His ascension into heaven, and sitting at the right hand of Thee, our God and Father, and His second glorious and awful appearing, when He shall come again with glory to judge the quick and the dead, and render to every one according to His works; even we, sinful men, offer unto Thee, O Lord, this dread and bloodless sacrifice, praying that Thou wilt not deal with us after our sins, nor reward us according to our iniquities;
But that Thou, according to Thy mercy and Thy unspeakable loving-kindness, passing by and blotting out the handwriting against us Thy suppliants, wilt grant to us Thy heavenly and eternal gifts (which eye hath not seen, and ear hath not heard, and which have not entered into the heart of man ) that thou hast prepared, O God, for those who love Thee; and reject not, O loving Lord, the people for my sake, or for my sinÃ¢â‚¬â„¢s sake:
Then he says, thrice: For Thy people and Thy Church supplicate Thee.
The People: Have mercy on us, O Lord our God, Father Almighty.
Again the celebrant says (Invocation): Have mercy upon us, O God Almighty. Have mercy upon us, O God our Saviour. Have mercy upon us, O God, according to Thy great mercy, and send forth on us, and on these offered gifts, Thy all-holy Spirit.
Then, bowing his neck, he says: The sovereign and quickening Spirit, that sits upon the throne with Thee, our God and Father, and with Thy only-begotten Son, reigning with Thee; the consubstantial and co-eternal; that spoke in the law and in the prophets, and in Thy New Testament; that descended in the form of a dove on our Lord Jesus Christ at the river Jordan, and abode on Him; that descended on Thy apostles in the form of tongues of fire in the upper room of the holy and glorious Zion on the day of Pentecost: this Thine all-holy Spirit, send down, O Lord, upon us, and upon these offered holy gifts;
And rising up, he says aloud: That coming, by His holy and good and glorious appearing, He may sanctify this bread, and make it the holy body of Thy Christ.
The People: Amen.
The celebrant: And this cup the precious blood of Thy Christ.
The People: Amen.