Jesus Christ established this sacrament the night before he was betrayed. He sat down with His disciples after having washed the feet of His disciples, and during the Passover Dinner, He took a cup of wine and said: "Drink of it all this is my blood, which is shed for you and for the remission of your sins."
Then He took the bread and said: "Take it, this is my body, which is broken for you and for the remission of your sins, do this in memory of me."
Since that night, all the first Christians were receiving this Holy Communion from the hands of the Disciples or priests or deacons. Prayers and hymns were then performed before and after receiving the Holy Communion leading to the creation of the Divine Liturgy. In these prayers explains the greatness and the holiness of the action. The Divine Liturgy that we celebrate every Sunday and Feast Day is performed for the Holy Communion, which is the heart of the Divine Liturgy. The bread and the wine are transformed with the power of the Holy Spirit during Divine Liturgy and become the Body and Blood of Jesus Christ.
The Orthodox Church never taught or believed that the bread and the wine represents the Body and Blood of Christ but IS the Body and Blood of Christ. At the Last Supper, Jesus Christ did not say this represents my body and this represents my blood, but He said: "This is my body and this is my blood." The Sacrament of the Holy Communion is Christ Himself. It is the most sacred Sacrament, where the faithful is united with His Lord and Savior. Just as the Holy Spirit descended to the womb of Mary and made the body of Jesus from the flesh of the Virgin, so the same Spirit descends upon the bread and wone on the altar, transforming them into the Body and Blood of Jesus.
Non-orthodox cannot receive Holy Communion in the Orthodox Church. All who receive Holy Communion from the same cup have to confess the same faith, the common faith. An Orthodox faithful is also not allowed to receive Holy Communion from another Christian Church. If the orthodox person does this, this means that he denies the orthodox teachings and becomes heretic. As long as we have dogmatic differences with the other denominations of Christianity, we cannot receive from the same cup.
