St. Thomas calls the Eucharist the miracle of miracles.
To be convinced of this, it is necessary only to reflect on what the faith of the Church teaches concerning this mystery. The first of the wonders operated in the Eucharist is transubstantiation. Jesus first, and then His priests, by His order and His institution, take the bread and the wine, pronounce over that material substance the words of consecration, and immediately all the substance of the bread, all the substance of the wine disappears. It has been changed into the sacred Body and the adorable Blood of Jesus Christ! Under the species of bread, as well as under that of the wine, is found truly, really, and substantially the glorified Body of the Saviour.
Of the bread, of the wine, there remain but the appearance, the color, the taste, the weight. As far as the senses are concerned, it is still bread, still wine. But faith tells us that it is the Body and the Blood of Jesus, veiled under the accidents, which subsist only by a miracle. It is a miracle that can be wrought only by the Almighty, for it is contrary to ordinary laws that the qualities of bodies should exist without the body that sustains them. Therein is the work of God. His will is their reason for existence. God can do all that He wills. He requires no more effort than to will. Behold the first wonder of the Eucharist.