To celebrate Pentecost, I would like to post a passage from Pope Benedict XVI's post-synodal exhortation, Sacramentum Caritatis (Sacrament of Charity), which concerns the relationship between the Holy Spirit and the Eucharist (sections 12 and 13). This portion of the document can be found at the Vatican's website here.
Jesus and the Holy Spirit
12. With his word and with the elements of bread and wine, the Lord himself has given us the essentials of this new worship. The Church, his Bride, is called to celebrate the eucharistic banquet daily in his memory. She thus makes the redeeming sacrifice of her Bridegroom a part of human history and makes it sacramentally present in every culture. This great mystery is celebrated in the liturgical forms which the Church, guided by the Holy Spirit, develops in time and space. (23) We need a renewed awareness of the decisive role played by the Holy Spirit in the evolution of the liturgical form and the deepening understanding of the sacred mysteries. The Paraclete, Christ's first gift to those who believe, (24) already at work in Creation (cf. Gen 1:2), is fully present throughout the life of the incarnate Word: Jesus Christ is conceived by the Virgin Mary by the power of the Holy Spirit (cf. Mt 1:18; Lk 1:35); at the beginning of his public mission, on the banks of the Jordan, he sees the Spirit descend upon him in the form of a dove (cf. Mt 3:16 and parallels); he acts, speaks and rejoices in the Spirit (cf. Lk 10:21), and he can offer himself in the Spirit (cf. Heb 9:14). In the so-called "farewell discourse" reported by John, Jesus clearly relates the gift of his life in the paschal mystery to the gift of the Spirit to his own (cf. Jn 16:7). Once risen, bearing in his flesh the signs of the passion, he can pour out the Spirit upon them (cf. Jn 20:22), making them sharers in his own mission (cf. Jn 20:21). The Spirit would then teach the disciples all things and bring to their remembrance all that Christ had said (cf. Jn 14:26), since it falls to him, as the Spirit of truth (cf. Jn 15:26), to guide the disciples into all truth (cf. Jn 16:13). In the account in Acts, the Spirit descends on the Apostles gathered in prayer with Mary on the day of Pentecost (cf. 2:1-4) and stirs them to undertake the mission of proclaiming the Good News to all peoples. Thus it is through the working of the Spirit that Christ himself continues to be present and active in his Church, starting with her vital centre which is the Eucharist.
The Holy Spirit and the eucharistic celebration
13. Against this backdrop we can understand the decisive role played by the Holy Spirit in the eucharistic celebration, particularly with regard to transubstantiation. An awareness of this is clearly evident in the Fathers of the Church. Saint Cyril of Jerusalem, in his Catecheses, states that we "call upon God in his mercy to send his Holy Spirit upon the offerings before us, to transform the bread into the body of Christ and the wine into the blood of Christ. Whatever the Holy Spirit touches is sanctified and completely transformed" (25). Saint John Chrysostom too notes that the priest invokes the Holy Spirit when he celebrates the sacrifice: (26) like Elijah, the minister calls down the Holy Spirit so that "as grace comes down upon the victim, the souls of all are thereby inflamed" (27). The spiritual life of the faithful can benefit greatly from a better appreciation of the richness of the anaphora: along with the words spoken by Christ at the Last Supper, it contains the epiclesis, the petition to the Father to send down the gift of the Spirit so that the bread and the wine will become the body and blood of Jesus Christ and that "the community as a whole will become ever more the body of Christ" (28). The Spirit invoked by the celebrant upon the gifts of bread and wine placed on the altar is the same Spirit who gathers the faithful "into one body" and makes of them a spiritual offering pleasing to the Father (29).