Christ instituted the Holy Eucharist in this way: He took bread, blessed and broke it, and giving it to His Apostles, said: “Take and eat; this is My body”; then He took a cup of wine, blessed it, and giving it to them, said: “All of you drink this; for this is My blood of the new covenant which is being shed for many unto the forgiveness of sins”; finally, He gave His Apostles the commission: “Do this in remembrance of Me.”
1. When our Lord said, “This is My body,” the entire substance of the bread was changed into His body; and when He said, “This is My blood,” the entire substance of the wine was changed into His blood.
In the Holy Eucharist, we find the three essentials of a sacrament. The institution was at the Last Supper. The matter is bread and wine; the form consists of Our Lord’s words. The grace is a nourishing grace coming from the very body and blood of Christ, helping us to be more closely united to God and our fellowmen in supernatural charity.
2. After the substance of the bread and wine had been changed, only the appearances of bread and wine remained.
By the appearances of bread and wine we mean all those outward forms and accidentals, like color, taste, smell, weight, shape, and whatever else that appears to the senses. This is the double miracle of the Holy Eucharist: The changing from bread and wine into Jesus Christ, and the existence of the appearances of bread and wine without their substance.