There are two answers to this question. The first answer is that that’s how people served wine at the time of the Last Supper and for a long time afterward.
Vintners made wine very strong, like juices that we buy today in concentrated form. Wine was diluted with water at a civilized table (see Prov 9:5); only barbarians drank unmixed wine.
The second answer is that this custom of humble and ordinary beginnings has acquired a rich symbolic meaning. Some of the earliest Christian writers — as early as St. Justin Martyr in 150 AD — mentioned the “mixed cup.” For some, the wine and water represent the blood and water that poured from Jesus’ side on the cross (see John 19:31-34). As the priest pours the two elements, a devout Christian can’t help but remember this scene from the Scriptures.
Other interpreters saw the mixture as a symbol of God’s communion with us. Saint Clement of Alexandria, writing around 200 AD, emphasized the effects of Communion upon the individual who receives: “As wine is blended with water, so is the Spirit with man.” A few years later, in North Africa, St. Cyprian spoke of the mixed cup but emphasized Christ’s communion with the whole Church:
“The water is understood as the people while the wine shows forth the blood of Christ. When the water is mingled in the cup with wine, the people are united with Christ…. Once the water and wine are mingled in the Lord’s cup, the mixture cannot anymore be separated.”
There is something exact about the symbol: Christ is the wine; we are the bit of water. The main part of the sacrament is Christ really present, but communion does not happen without our willing participation.
The mixed chalice can also be seen as a sign of Christ’s two natures, divine and human, united in one person. The wine represents his divinity, the water his humanity. The two natures come to us together in the Eucharist, as they did in the Incarnation.
Thus from the earliest times the mixed chalice at Mass was emblematic of the mystery it held: the mystery of Christ and of salvation by his blood.
The Church has insisted on this mixing of the water with the wine for two millennia. In the 16th century, the Council of Trent even excommunicated priests who neglected to mix the elements. The Church has good reasons to be faithful here. Some are perhaps historical: a fidelity to a custom dating back to the time of Jesus. Others, however, are doctrinal, dealing with the mystery at the heart of the faith — the marvelous exchange spelled out in the prayer at the Offertory: “By the mystery of this water and wine, may we come to share in the divinity of Christ, who humbled himself to share in our humanity.”
MIKE AQUILINA is the author or editor of more than 40 books on Catholic history, doctrine and devotion. This column is reprinted with permission from his book “Understanding the Mass: 100 Questions, 100 Answers” (Servant Books, Cincinnati, 2011)
The miracles of the multiplication of the loaves, when the Lord says the blessing, breaks and distributes the loaves through his disciples to feed the multitude, prefigures the superabundance of this unique bread of his Eucharist.
The sign of water turned into wine at Cana already announces the hour of Jesus’ glorification. It makes manifest the fulfillment of the wedding feast in the Father’s kingdom, where the faithful will drink the new wine that has become the Blood of Christ.
Catechism of the Catholic Church, #1335