This question was posed to me the other day, why does the priest add that small drop of water with the wine at consecration?
We then began discussing that some priests use the tiniest drop while others will just splash some water in the chalice of wine. The simple explanation is that this is believed to have been the custom of the Jewish people. They would temper the wine with water according to the custom of that country. This would have been what Jesus did at the traditional Passover meal.
If we reflect on the invisible reality presented by the visible sign of the cup, the Lord's Passion comes immediately to mind. We remember that both water and blood flowed from the side of Christ when His heart was pierced. And this signifies our Baptism in Christ, to die to self so we can become one in Christ. At the point of the Mass, when the priest pours the water into the chalice, he recites almost sillently, "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."
Our Church Fathers believed the water is understood as the people and the wine is understood to be the blood of Christ. When the water is mixed with the wine, the people are made one with Christ. We are now cojoined with Christ and nothing can separate the two. We become the Body of Christ, cojoined with Him. It could never be just the wine or just the water, there must be a comingling of the two. I read that the Council of Trent felt this was so vital that whoever denied this practice of mixing the water and the wine was to be excommunicated. Who knew something we see at every Mass could have such an effect on us as Church.