I have always been told—and have always believed—that when Jesus cried, "It is finished!" he meant that his work in bearing the sins of the world was completed.
But it struck me about ten minutes ago that there is a problem with this: when Jesus uttered those words he was not dead (obviously). But the church affirms that Christ died for our sins. So it cannot literally be true that his cross-work was completed when he said those words. That was not finished—at least not in every respect.
This has some bearing on what we say about Christ's descent into Hades. This ancient belief has received a range of interpretations over the centuries, but the most basic division in the interpretations is between (a) the views in which Christ was thought to be among the dead as the victor proclaiming his triumph and (b) those in which he was among the deceased as one who "stood" in solidarity with the dead, suffering death's humiliation and Godforsakenness. Now one argument against the latter range of views is that Christ's humiliation ended on the cross—after all, he said that it was finished. So the descent could only be a victorious descent.
But if the words "It is finished!" do not mean that Christ has no more sin-bearing then the way is opened up to see the descent as an integral part of Christ's humiliation—his being dead.
That said, I see no reason why we need to play off (a) and (b) against each other. I think that the descent is a pivot element in the story and can be seen both in terms of humiliation and exaltation, cross and resurrection. That's for another time.
Anyway, here is my question: what is finished?