Is the Mass the same as Christ’s Sacrifice on the Cross, or is it a different Sacrifice?

It is the same Sacrifice. Christ offered Himself, once for all. “…[W]e are sanctified by the oblation of the Body of Jesus Christ once.” (Heb. 10:10).

To understand this, we have only to go back to the concept of oblation, renunciation, and choice. The renunciation is summarized by Christ’s death, accepted once and for all. On Calvary, this act of renunciation was made once, and it is passed.

But above all, our Lord’s Sacrifice consists in the constant desire for His Fathers will in preference to His own; and this preference remains eternally fixed in heaven. Suffering passes - the fact of having suffered remains.

It’s the same thing for us when we renounce anything. The act of self-denial is, like all acts, temporary; but the disposition of the will to deny its self for a greater good remains just so long as we do not take it back. Death fixes us forever in the dispositions which it finds us. Christ’s Sacrifice persists in heaven, because the legacy of His life made on the Cross has never been canceled. That which he gave was given for all time…. Christ’s immolation is eternal. St. John, in His vision of heaven, sees Jesus as “a lamb standing upright, yet slain (as I thought) in Sacrifice” (Apoc. 5:6) [Knox].

This is understandable. The purpose of our Lord’s Sacrifice having been to glorify God, the act whereby He glorifies Him must, of necessity, be eternal.

When the priest brings Christ down upon the altar, he renders Him present such as He is in heaven; and He is in heaven with the same loving dispositions that He had on Calvary at the moment of His death.

The Mass is, therefore, not a new Sacrifice by Christ; but the same Sacrifice actualized in the present. “We know that Christ rising again from the dead, dieth now no more.” (Rom. 6:9).

The Mass is thus the perpetual prolongation of the Sacrifice made on the cross. Consequently, every Mass is the one immolation of Christ repeated in the Act of Oblation. By the same act of the will, Jesus offers at the last supper His death in the future; on Calvary His death in the present; on heaven and on the altar His death in the past.

This special presence of Christ on the altar is peculiar to the Mass and demonstrates is grandeur.

When we celebrate the other mysteries of Christ’s life, we merely commemorate them. There is no real renewal of the mystery on the day devoted to it. At Christmas, the Church recalls to our minds the saviors birth, but this birth does not really take place - is not actualized in the present. On Ascension Thursday, our Lord does not renew His ascent into heaven. It is quite otherwise for the mass. It is no simple symbolic representation, for the same Sacrifice that Christ accomplished on the Cross is made truly present in an un-bloody manner on the altar.

(1962 Daily Roman Missal, Angelus Press)