The Eucharist as Medicine of Immortality(Following is my term paper of Spring 2010. I may revisit the topic again at a higher level in the future. I've seen a number of opportunities for improvement when I have the opportunity to write with more depth on the topic)
Since the second century, the Catholic Church has honored the sacrament of the Holy Eucharist under the title, “the medicine of immortality.” This teaching that the Eucharist is a medicine of immortality has been obscured or omitted from most catechesis. The concept that the Eucharist is the "medicine of immortality" is a universal Christian teaching of Eastern Christian origin that is a necessary article of faith to fully understand Church teaching on the Eucharist. Although the teaching has been officially taught by the teaching authority of the Church, it seldom percolates down to the laity. Along with a fuller catechesis that teaches that the Eucharist is truly the Body, Blood, Soul, and Divinity of Jesus, Catholics need this teaching of the “medicine of immortality” to form a more complete picture of the sacrament.
In his original unveiling of the Sacrament of Holy Communion, Jesus told us that, "Anyone who eats my flesh and drinks my blood has eternal life and I will raise him up on the last day.” This is clearest teaching on the Eucharist as a “medicine of immortality”. To call this a simple explanation would be disingenuous, as many of his disciples left him over this teaching, despite the tremendous and gratuitous promise He gave to us.
Perhaps the earliest written presentation of the “medicine of immortality” concept is in St. Ignatius of Antioch's letter to the Ephesians, a non-canonical epistle. This letter is nonetheless of value to Catholics as part of a body of work that helps to interpret the Scriptures by illustrating certain teachings that follow an unbroken continuity back to the earliest Apostles. Ignatius was a “Church Father” who studied at the feet of St. John, the beloved apostle, who in turn had studied at the feet of Christ. Ignatius called the Eucharist a vital, universal part of the faith. He promised to write to the Ephesians a second time, but only, “…if the Lord make known to me that you come together man by man in common through grace, individually, in one faith...breaking one and the same bread, which is the medicine of immortality, and the antidote to prevent us from dying, but [which causes] that we should live for ever in Jesus Christ.” The breaking of this bread continues to be the most important act of worship in the Church.
St. John's Gospel tells us that many things that Jesus did and said had to be left out of the book for brevity's sake, so it is conceivable that Christ himself might be the originator of the concept that His body and blood are the medicine of immortality given to us in the Eucharist. Indeed, St. Luke (notably a physician) and St. Matthew both recount the anecdote of Jesus telling the Pharisees, “Those who are healthy do not need a physician, but the sick do.” Christ Himself is the Divine Physician who gives us a remedy for death, His Body and Blood to eat. He enables us to one day have eternal life. If we are sinners who are “sick” with sin, our Divine Physician’s medicine of choice has been identified by His earliest Apostles as the Holy Eucharist.
Apocalyptic Scripture alludes to Christ providing a source of a medicine of great power. In the Bible, the prophet Ezekiel spoke of a temple, which we can presume to represent Christ, from whose side flowed water toward the east and then south.
"This water flows into the eastern district down upon the Arabah...Wherever the river flows, every sort of living creature that can multiply shall live...Along both banks of the river, fruit trees of every kind shall grow; their leaves shall not fade, nor their fruit fail. Every month they shall bear fresh fruit, for they shall be watered by the flow from the sanctuary. Their fruit shall serve for food, and their leaves for medicine."
St. John tells us in his book of Revelation that he was shown by an angel a scene that was a clear parallel to this prophet's vision. John clearly identifies the source of the water:
“Then the angel showed me the river of life-giving water, sparkling like crystal, flowing from the throne of God and of the Lamb down the middle of its street. On either side of the river grew the tree of life that produces fruit twelve times a year, once each month; the leaves of the trees serve as medicine for the nations. Nothing accursed will be found there anymore. The throne of God and of the Lamb will be in it, and his servants will worship him.”
By the time these words were committed to the page, the apostles had already begun the evangelization of all peoples, bringing this Blessed Sacrament to the lips of all nations. This passage in Revelation has multiple beauties about it. When Christ's side and heart were pierced, blood and water flowed from the wound, becoming our Baptism and Eucharist. This vision of a throne issues water from its side, nourishing the tree of life, a clear illustration of how Christ’s grace provides us with the Holy Eucharist.
Christ's cross is the tree of life, the contrast to the tree in the Garden of Eden that brought death to mankind. The fruit and leaves of this tree of life are together the Eucharist that nourishes us and at the same time is our medicine for all nations. Among those who worship Christ it is a particular grace to be able to receive the produce of this tree with the opportunity to share in eternal life with Christ.
As Prefect of the Congregation for Divine Worship and the Discipline of the Sacraments, Francis Cardinal Arinze remembered St. Ignatius’ words, giving us a rare exposition of the doctrine. He tells us simply that in the Eucharist, Christ gives us “a pledge of eternal life, of our bodily resurrection, since Jesus promised that those who so receive him in this sacrament have eternal life and he will raise them up at the last day. Therefore St. Ignatius of Antioch called Holy Communion ‘a medicine of immortality, and antidote of death.’”  Arinze takes it as a given that the Eucharist is a medicine even while it is the sacrament of the altar.
The medicine of immortality analogy is still accepted today, having been listed in the Catechism parallel to other names for Holy Communion, “the bread of angels, bread from heaven, medicine of immortality, viaticum.” The medicine of immortality is also named in like manner in John Paul II's Ecclesia De Eucharistia. For his part, Pope Benedict XVI sees an additional strong tie between the Eucharist and the sacrament of Anointing of the Sick. The latter is given to those in such circumstances as imminent death, along with viaticum, the Eucharist given as “bread for the journey” toward Heaven. Benedict states in Sacramentum Caritatis that. “On their journey to the Father, communion in the Body and Blood of Christ appears as the seed of eternal life and the power of resurrection.” 
The graces that we receive by taking and consuming the Eucharist are a medicine for the soul. Just as a medicine conforms the body to health, the Eucharist conforms our fallen nature to Christ. It is the stronger substance that turns us into Christs; instead of just being consumed as normal bread, it acts on and consumes those who eat the Eucharist.
It is important for us to go to Christ the physician to be healed. Church discipline has long prescribed a period of fasting before receiving the Eucharist, just as a surgeon requires the same of his patient before surgery. Our fasting better prepares us by causing us to hunger for the Eucharist, allowing Christ's hands to work on our souls. Just as "God formed our inmost beings and knit us in the womb", He also repairs our inmost beings through such means as this medicine of immortality.
For those who revere Christ, there are practical benefits to receiving a medicine that brings us to eternal life. The benefits may not be recognized as immediate, but the effects are certainly lasting, indeed eternal. In the short term of mortal life, the availability of the Eucharist prepares us for Heaven and teaches us to avoid sin. Like periodic Confession, frequent Communion encourages us to seek and to stay in a state of grace by avoiding sin and cultivating an active prayer life, which better disposes us to face our final judgment. So, just as His disciples asked Christ, “Sir, give us this bread always,” we must also ask our Lord to give us this same gift, this medicine of immortality in the Eucharist.
 John 6: 54 (NAB)
 St. Ignatius of Antioch, “The Epistle of Ignatius to the Ephesians”, New Advent [website]; available from http://www.newadvent.org/fathers/0104.htm (accessed 21 April, 2010).
 Luke 5:31 (NAB)
 Ezekiel 47: 9-12 (NAB)
 Revelation 22:1-3 (NAB)
Francis Cardinal Arinze. “The Holy Eucharist Unites Heaven and Earth,” September 25, 2004, USCCB, http://www.usccb.org/liturgy/arinze.shtml (accessed April 22, 2010).
 Catechism of the Catholic Church Second Edition, Libreria Editrice Vaticana, (1997), 1331.
 John Paul II, Encyclical Letter Church of the Eucharist (Ecclesia De Eucharistia), April 17, 2003, #18, Vatican, http://www.vatican.va/holy_father/special_features/encyclicals/documents/hf_jp-ii_enc_20030417_ecclesia_eucharistia_en.html (accessed April 22, 2010).
 Benedict XVI, Post-Synodal Apostolic Exhortation Sacrament of Charity (Sacramentum Caritatis), February 22, 2007, #22, Vatican, http://www.vatican.va/holy_father/benedict_xvi/apost_exhortations/documents/ hf_ben-xvi_exh_20070222_sacramentum-caritatis_en.html (accessed April 22, 2010).
 Psalm 139:13 (NAB)
 John 6:34 (NAB)