This is the most precious and sacred moment of the entire Divine Liturgy. All the people kneel, unless kneeling is not appropriate for the season as is the case from Easter to Pentecost. Since this is a season of great joy and happiness, while the Priest asks the Holy Spirit to change the bread and wine into the Body and Blood of Jesus Christ. Even though outwardly they may appear to be still bread and wine, they are now the Real Body and the Real Blood of Jesus.
The Orthodox Church has never attempted to explain in philosophical or any other terms how this change takes place, but this is the Orthodox Church's belief without any qualifications, and this is her unchanging teaching. We must have a full understanding and complete realization of this fact; otherwise, Holy Communion can never provide the spiritual strength and uplifting exaltation that it should.
Our attitude as we kneel during the Epiclesis or Prayer of Invocation should represent the highest form of spiritual receptiveness and devotion of which we are capable. We have prepared for it by visualizing the scene at Golgotha, Christ's death on the Cross. In dying on the Cross for us, He took our place. We in turn take the place of those who stood at the foot of the Cross. We try to after love, devotion, and humility. The eyes of our souls must try to visualize Jesus descending in that moment from Heaven and imparting His Body to the bread on the Diskos and His Blood to the wine in the Cup, thus once again offering Himself to the faithful as He did at the Last Supper with His Disciples.
Whether we are prepared to receive Holy Communion or not, our hearts and souls should be filled with spiritual joy and exaltation and thankfulness as Jesus offers Himself to us with His undying love. This is what transpires in the Divine Liturgy, and this is what should be in our souls and minds as the choir sings "We praise Thee" and we kneel before our Saviour to ask Him for understanding and guidance and help in all our needs. The Epiclesis is followed by prayers remembering all those who have gone before us, especially the Holy Virgin Mary, the Theotokos, in whose honour the choir sings a beautiful hymn.