In regards to propitiation, the New Covent going into effect: and our sins being paid,
what took place on the Cross that did not take place at the Last Supper?
That depends on what you mean.
But if you want a simple answer, here it is: NOTHING.
Want an explanation? Read below.
In ESSENCE, that is, in SUBSTANCE, in PRINCIPLE, in PATTERN, the Last Supper and the Cross event are one in the same sacrifice. There is only one sacrifice of Christ, not many. Thus, the Last Supper and the Cross cannot in principle, cannot in essence, cannot in substance, cannot in pattern be a different sacrifice. If they were, there would be two different and competing sacrifices of Christ which is impossible.
There is but ONE sacrifice of Christ.
The question then, is what is DIFFERENT on the cross vs. the Last Supper?
The difference between the Last Supper and the Cross is not in the sacrifice itself, but in HOW the sacrifice is presented; that is, the MANNER or MODE in which the sacrifice is presented.
At the Last Supper, the sacrifice is presented in SACRAMENTAL form; that is, it is presented in an unbloody, unfleshy manner, a manner that does NOT, I repeat, DOES NOT involve the suffering and physical death of Christ. On the cross, the the sacrifice is presented in a physical and EARTHLY manner; a manner that involves suffering and death. This presentation of the sacrifice is UNIQUE, NEVER TO HAPPEN AGAIN, NEVER TO BE REPEATED. Christ suffers and dies ONCE and ONLY ONCE.
When Mass is celebrated, a sacrifice takes place, namly, that of Christ. However, Christ is glorified and thus, does not suffer and die in the sacrifice of the Mass.
The problem with Protestants in understanding this is twofold in my opinion. 1) the Nominalism in which they are unwittingly steeped and perhaps more importantly, 2) Their identification of the Sacrifice with the CROSS, rather than Jesus himself.
In the system of Nominalism, universals do not exist; they are just names we assign things for the sake of convenience. Only particulars exist. Becasue if this, it is understandable why Protestants think each Mass is a "re-sacrifice" of Christ, and why they would see the presence of Christ in the hosts as multiplied in thousands of hosts throughout the world, and why they would see Jesus as a prisoner in the tabernacle. If only particulars exist, it is impossible for the sacrifice of Christ to be ONE yet----"many." In other words, it is impossible for there to be ONE sacrifice of Christ, yet many presentations of that ONE sacrifice.
As for point 2: Christ himself IS, note the use of the verb to be--as in present tense, the sacrifice. Christ did not offer himself (past tense) Christ will not offer himself at some point in the future, Christ IS the sacrifice. On the cross, Christ IS the sacrifice. In the resurrection Christ IS the sacrifice. The resurrection is not something fundamentally different than the sacrifice. The resurrection IS the sacrifice perfected. It is why the Mass is possible.
For Protestants, however, they seem to think the resurrection is something different in kind from the sacrifice itself. They do not see the identification of the cross with the resurrection. They think the cross is one thing, the resurrection another. They aren't. They are one in the same reality.