But why do we still need a sacrifice if Jesus’ sacrifice on the cross was sufficient. He did say “It is finished” I believe.
There’s a lot of ground to cover, in answering this question. It’s probably the most important question to ask, in the context of what Jesus meant regarding the ‘memorial’ of the Last Supper and His commands to ‘eat my body and drink my blood’!
Part of the discussion has to happen on the level of language – that is, what exactly does the Greek of the Gospels tell us: after all, the evangelists were using all the tools that the Greek language gave them, and therefore, we need to understand all the subtleties that were at their disposal and which they utilized!
First, though, a question: if “it is finished” meant what you say it means, then wouldn’t that make Jesus a liar – or at least, horribly inconsistent? If, in the Gospel of John, He says “you must eat my body and drink my blood or else you have no life in you”, and at the Last Supper He identifies the Passover bread and wine as His body and blood, and then, on the cross, He says “it is finished”, then doesn’t this mean that He set up a requirement for us that He completely made impossible for us to fulfill? I mean, there wasn’t a whole lot of time between Holy Thursday and Good Friday to have this memorial meal, and if “it is finished” means “sorry, no more memorials now”, then He’s kind of left us in the lurch, hasn’t He? After all, no “body and blood” means “no life within you,” doesn’t it?
Let’s look at the Greek, though: the sentence Jesus uttered (in John 19:30) is “Τετέλεσται.” Sometimes, it’s translated as “it is finished,” but there’s more to the story than that. That word – in that form – is used in only one other place in the Gospels: John 19:28 (“After this, Jesus knowing that all things were now accomplished, that the scripture might be fulfilled, saith, I thirst.”) Here, the word ‘accomplished’ is used as the translation. There’s still another place to see the root word (telos) used, though: in Mt 5:48, Jesus tells us “be perfect, as your heavenly father is perfect.” So, which is it? Does
telos mean ‘perfect’ or ‘accomplished’ or ‘finished’? In fact, a
telos is a ‘goal’ – so Jesus means that God perfectly fulfills the goal of His existence, and we should strive to do the same. In John 19, then, the use of
τετέλεσται conveys that sense of ‘completion’ or ‘goal-achievement’. Jesus tells us that His redemptive sacrifice of self has reached fulfillment.
What does that mean for us, though, in the context of the Eucharist? Well, as Micosil points out, our ‘sacrifice’ of the Eucharist is not a re-sacrificing of Christ: that happened once and for all. What it
is, however, is a re-presentation of the sacrifice of Christ, so that we actually
are doing a Semitic-style memorial – one in which the action of the sacrifice is memorialized and re-presented, so that the act itself is brought to mind.
It would be odd, then, to suggest that, since Jesus asked for a memorial of the offering of His body and blood – on a night in which Jews re-present a memorial of the Passover event in Egypt! – be eschewed simply because Jesus pronounced His sacrifice to be efficacious as He died on the cross!