Encyclical Letter on the Holy Eucharist - Pope John Paul II Parts 16 & 17

16. The saving efficacy of the sacrifice is fully realized when the Lord's body and blood are received in communion. The Eucharistic Sacrifice is intrinsically directed to the inward union of the faithful with Christ through communion; we receive the very One who offered himself for us, we receive his body which he gave up for us on the Cross and his blood which he “poured out for many for the forgiveness of sins” (Mt 26:28). We are reminded of his words: “As the living Father sent me, and I live because of the Father, so he who eats me will live because of me” (Jn 6:57). Jesus himself reassures us that this union, which he compares to that of the life of the Trinity, is truly realized. The Eucharist is a true banquet, in which Christ offers himself as our nourishment. When for the first time Jesus spoke of this food, his listeners were astonished and bewildered, which forced the Master to emphasize the objective truth of his words: “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink his blood, you have no life within you” (Jn 6:53). This is no metaphorical food: “My flesh is food indeed, and my blood is drink indeed” (Jn 6:55).

17. Through our communion in his body and blood, Christ also grants us his Spirit. Saint Ephrem writes: “He called the bread his living body and he filled it with himself and his Spirit... 

He who eats it with faith, eats Fire and Spirit... Take and eat this, all of you, and eat with it the Holy Spirit. For it is truly my body and whoever eats it will have eternal life”.²⁷ The Church implores this divine Gift, the source of every other gift, in the Eucharistic epiclesis. In the Divine Liturgy of Saint John Chrysostom, for example, we find the prayer: “We beseech, implore and beg you: send your Holy Spirit upon us all and upon these gifts... that those who partake of them may be purified in soul, receive the forgiveness of their sins, and share in the Holy Spirit”.²⁸ And in the Roman Missal the celebrant prays: “grant that we who are nourished by his body and blood may be filled with his Holy Spirit, and become one body, one spirit in Christ”.²⁹ Thus by the gift of his body and blood Christ increases within us the gift of his Spirit, already poured out in Baptism and bestowed as a “seal” in the sacrament of Confirmation.