Venerable Fulton Sheen
“In the Mass, the faithful are already present on the altar under the appearance of bread and wine. At the moment of the Consecration of the Mass, when the priest as Christ pronounces the words ‘This is My Body’ and ‘This is My Blood,’ the substance of the bread becomes the substance of the body of Christ, and the substance of the wine becomes the substance of the blood of Christ. At that moment, the faithful are saying in a secondary sense with the priest: ‘This is my body; this is my blood. Take it! I no longer want it for myself. The very substance of my being, my intellect, and my will–change! Transubstantiate!–so that my ego is lost in Thee, so that my intellect is one with Thy Truth, and my will is one with Thy desires! I care not if the species or appearances of my life remain; that is to say, my duties, my avocation, my appointments in time and space. But what I am substantially, I give to Thee.'”
Source: Ven. Fulton Sheen, These are the Sacraments