Catholic Doctrine: The Sacrament of the Eucharist
The word Eucharist means “excellent grace” or “thanksgiving.” This word points out the divine gift of the Redemptor and the mystery of the Faith in which, under the species of bread and wine, Jesus Christ Himself is contained, offered, and taken as food. The Eucharist is at the same time a sacrifice and a sacrament of the New Law.
Institution of the Holy Eucharist
Our Lord Jesus Christ instituted the Holy Eucharist during the Last Supper, before His Passion, when He took bread, blessed it, and gave it to His disciples, saying to them, “Take and eat, this is my body,” and after, taking the cup, He gave it to them, saying, “Drink, this is my blood,” and He added, “Do this in memory of me” (Cf. Mt. 26:26-28; Mk. 14:22-24; Lk. 22:19-20; I Cor. 11:23-25).
When Jesus pronounced the words of consecration over the bread and wine, He performed a marvelous and singular conversion of the entire substance of the bread into the Body of, and the entire substance of the wine into the Blood of Jesus Christ, while only the form of bread and wine remained.
This conversion is called transubstantiation.
The species designates the quantity, the figure or aspect, the odor, the color, the taste, and all the other properties of bread and wine which fall under our senses. But the substance is no longer that of bread nor that of wine; it is entirely that of Jesus Christ, really present in His Body, Blood, Soul, and Divinity.