For the death He died He died to sin, once for all, but the life He lives He lives to God. (Rom 6:10)Repeatedly we get this message that Christ sacrificed Himself "once for all". So, we get it. All sin is paid for because His sacrifice was "once" for all sin, right?
He has no need, like those high priests, to offer sacrifices daily, first for His own sins and then for those of the people, since He did this once for all when He offered up Himself. (Heb 7:27)
Nor was it to offer Himself repeatedly, as the high priest enters the holy places every year with blood not his own, for then he would have had to suffer repeatedly since the foundation of the world. But as it is, He has appeared once for all at the end of the ages to put away sin by the sacrifice of Himself.
And by that will we have been sanctified through the offering of the body of Jesus Christ once for all. (Heb 10:10)
While this would appear to be a reasonable conclusion and, in fact, a popular one, it only takes a moment to figure out we're in trouble. You see, if all sin is paid for, then no one can justly be condemned for their sin. Thus, all that stuff in Scripture, even from the lips of Jesus, is nonsense -- stuff about damnation and eternal torment and all that. "Saved by faith" is nice, but pointless since all sin is already paid for, you see? A just God cannot consign to Hell people who are now blameless because their sins were paid in full. So the Universalists are right and our message of "repent and believe" is unnecessary. Everyone has made it. Oh, and Scripture contradicts itself, so it is unreliable.
Is that what is meant by this phrase in this application? Does this "once for all" require "paid once for all sin"? I don't think so. Logic doesn't require it. It simply requires that something was done once that would take care of all of something else. The phrase doesn't give you the object. Once for all what?
I think you'll find the answer to that question in that last passage in Hebrews 10. A few verses later we read
For by a single offering He has perfected for all time those who are being sanctified. (Heb 10:14)Same two pieces. "A single offering" -- once. "Perfected for all time" -- all. But note that this single offering did not perfect for all time everyone. It doesn't claim to have covered all sin. It claims to have perfected all "who are being sanctified". Thus, this "once for all" isn't talking about covering all sin, but covering all sin for all those who are "being sanctified" -- for the elect.
What's the point? In the phrase, "once for all", in these texts, the point is not "all", but "once". Prior to Christ's death and resurrection, sin was paid for repeatedly. Christ's sacrifice was better. It occurred once and all the sin He intended to cover was actually covered -- once for all.
What's the point? Christ's sacrifice is better than the sacrifices of the Old Covenant. We have absolute assurance that the single sacrifice of the sinless Christ ("once") produced complete satisfaction for sin for all who are in Christ ("for all"). "There is therefore now no condemnation for those who are in Christ Jesus." (Rom 8:1) Incredibly good news!
What's the point? Scripture is important and true -- God's Word. Be careful, when you find what appears to be a contradiction. In this example, it was the apparently clear reading that all sin is paid for by Christ's sacrifice over against the very clear statements that there is condemnation for those not in Christ. You can choose to reject both as obviously contradictory and discard the Bible as reliable. You can choose to hold on to contradictions, living in cognitive dissonance, not actually finding the truth. Or you can examine it with the prior commitment that God's Word is true and arrive at an actual answer. It's called "rightly handling the word of truth." (2 Tim 2:15)