The Mass Is a Real Sacrifice

The objection is solid: Hebrews says Christ died 'once for all' (Hebrews 10:10). So isn't calling the Mass a sacrifice repeating something that's finished?

No, and that's the key. The Mass doesn't repeat Calvary; it re-presents it, makes it present. The one sacrifice of Jesus, offered once in history, is the same sacrifice made sacramentally present on the altar so we can actually enter into it. The Catechism puts it plainly: the Eucharist is 'a sacrifice because it re-presents (makes present) the sacrifice of the cross' and because it 'applies its fruit' (CCC 1366). Same victim. Same offering. Only the manner differs.

Notice Hebrews 13:10 doesn't say 'we have a table.' It says 'we have an altar.' That word matters. Aquinas reads it as pointing directly to the cross: 'That altar is the cross of Christ, on which he was immolated.' And centuries earlier, God promised through Malachi that 'in every place incense is offered to my name, and a pure offering' would be made among all the nations (Malachi 1:11). Irenaeus and the early Church read that prophecy as fulfilled in the Eucharist, the sacrifice offered everywhere the Church gathers. Liturgical scholars have called it the key Eucharistic text of the first three centuries.

Pius XII nailed the distinction in Mediator Dei: the Mass is 'no mere empty commemoration' but 'a true and proper act of sacrifice.' His exact words: 'It is one and the same victim; the same person now offers it… the manner of offering alone being different.' No repetition. No multiplication. The Cross is not re-opened as a new wound. It's re-presented, its fruit applied, its memory kept alive until Christ comes again. That's not a memorial meal. That's a living sacrifice.