"It is Finished"...Unless It Isn't?

In the past week I got into a Facebook conversation where a person attempted to claim that Catholics do not believe that "Christ is sufficient for our salvation." Catholics believe you need things like Sacraments, Popes, Mary, etc, added to Christ in order to be saved. I asked him to provide any church documents which stated that Christ was not sufficient and as of yet, I have not received any. I'm not holding my breath.

When I asked him why the people on this person's Facebook wall believe that Catholics do not believe in the sufficiency of Christ, I was given this comment which I am paraphrasing since there were multiple variations of the same basic statement;

Because Christ said 'it is finished' from the cross. He didn't say you still need to do stuff he said, 'it is finished' and 'it is finished' means 'IT IS FINISHED.'

The all caps it is finished was not paraphrased. So what is the answer to this question?

Christ does say 'it is finished', but He doesn't say what 'it' is. To say that 'it' means salvation is an interpretation of the text. Christ didn't say 'salvation is finished' he said, 'it' is finished. We have to know what 'it' is. So what is 'it'?

We can know what 'it' is not. 'It' certainly is not salvation. Christ can’t be talking about Salvation from the cross because salvation is not yet possible. In 1 Cor 15 Paul says that if not for the Resurrection our faith would be in vain.

“If there is no resurrection of the dead, then not even Christ has been raised…For if the dead are not raised, then Christ has not been raised either. And if Christ has not been raised, your faith is futile; you are still in your sins.”

So we are forced to draw two conclusions if we say that Salvation was sufficiently won when Christ said “it was finished.” Either Paul is a liar when he says that without the Resurrection we would still be in our sins or Christ is not referring to salvation when he says 'it'.

Since God is the primary author of Scripture and He can never tell a lie, it cannot be option #1. We are then forced, by logical necessity, to draw the conclusion that 'it' is not salvation, but something else.

So what then does “it” in the “it is finished” mean?