After the elevation of the eucharistic gifts to the Father, the celebrant of the Divine Liturgy prays for the Holy Spirit to come upon them, and upon all of the people, and to change (or as the Liturgy of St. Basil says, to show) the bread and wine offered in remembrance of Christ to be the very Body and Blood of the Lord.
The prayer for the coming of the Holy Spirit is considered by the Orthodox to be an essential part of the Divine Liturgy. It is called the epiklesis, which means literally the calling upon or the invocation.
The Orthodox Church believes, as it prays, that the Holy Spirit is always “everywhere and fills all things.” The invocation of the Holy Spirit at the Divine Liturgy is the solemn affirmation that everything in life which is positive and good is accomplished by the Spirit of God. Creation, salvation, eternal glorification; the entire work of God in making and saving the world is accomplished by the power of the Holy Spirit. He is the one who dwelt in Jesus making him the Christ. He is the one by whom Christ was incarnate of the Virgin Mary. He is the one who led Christ to the cross as the innocent Victim, the one who raised him from the dead as the triumphant Victor.
He is the one who guarantees the indwelling of God with men in the Holy Communion of the Church and in the life of the Kingdom to come.
Again we offer unto Thee this reasonable and bloodless worship, and we ask Thee, and pray Thee, and supplicate Thee: Send down Thy Holy Spirit upon us and upon these gifts here offered. And make this bread the precious Body of Thy Christ.
And that which is in this cup, the precious Blood of Thy Christ.
Making the change by the Holy Spirit.
That these gifts may be to those who partake for the purification of soul, for remission of sins, for the communion of the Holy Spirit, for the fulfillment of the Kingdom of Heaven; for boldness towards Thee, and not for judgment or condemnation.
In the Orthodox Churches of the Slavic tradition, the Prayer of the Third Hour is added to the epiklesis. It is a prayer asking the Lord to send the Holy Spirit to the Church right now as he did “at the third hour” to his holy apostles and disciples on Pentecost. This prayer was added to emphasize the necessity of the Holy Spirit in the sacramental action of the Divine Liturgy, and to affirm that nothing at all may be done in Christ without the specific intervention of the Spirit of God.