Štěpán Martin Filip reconstructs St. Thomas Aquinas’s account in Summa theologiae III, q. 83, a. 1, asking how the Mass can be a true sacrifice when Christ’s Passion is one historical and unrepeatable offering. Aquinas calls the Eucharist a sacrifice because it is the representative image and memorial of the Passion and because it communicates the fruits of that redemption. The Eucharist is simultaneously sacrament and sacrifice: it is received as a sacrament and offered to God as a sacrifice, with sacrifice distinguished from oblation by an action performed upon what is offered. The study explains why “image,” “representation,” “figure,” and “remembrance” do not reduce the Mass to an empty symbol. The whole liturgy recalls Christ’s death, but the essential sacrificial act is the consecration of bread and wine. Their separate consecration represents the separation of Christ’s body and blood in death, while Christ is truly present—body, blood, soul, and divinity—through consecration and concomitance. The Mass therefore does not repeat the Cross physically; it sacramentally represents the one sacrifice and applies its saving power. Other rites enrich this representation, while the consecration constitutes its sacrificial essence, with communion completing the rite’s integrity.